diff --git a/.travis.yml b/.travis.yml
index ea5477487..9f1d5d847 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -29,3 +29,5 @@ script:
   - ./bin/console lint:xliff translations
   # this checks that the application doesn't use dependencies with known security vulnerabilities
   - ./bin/console security:check --end-point=http://security.sensiolabs.org/check_lock
+  # this checks that the composer.json and composer.lock files are valid
+  - composer validate --strict
diff --git a/composer.lock b/composer.lock
index 7cffee280..6b9c7a366 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
         "This file is @generated automatically"
     ],
-    "content-hash": "4bb9e80aa633f2acfe6511b678d8a05c",
+    "content-hash": "376bb830795bbcf2fe597a487ea961ff",
     "packages": [
         {
             "name": "composer/ca-bundle",
@@ -1763,63 +1763,6 @@
             "homepage": "https://symfony.com",
             "time": "2017-07-29T21:54:42+00:00"
         },
-        {
-            "name": "symfony/browser-kit",
-            "version": "v3.3.9",
-            "source": {
-                "type": "git",
-                "url": "https://github.com/symfony/browser-kit.git",
-                "reference": "aee7120b058c268363e606ff5fe8271da849a1b5"
-            },
-            "dist": {
-                "type": "zip",
-                "url": "https://api.github.com/repos/symfony/browser-kit/zipball/aee7120b058c268363e606ff5fe8271da849a1b5",
-                "reference": "aee7120b058c268363e606ff5fe8271da849a1b5",
-                "shasum": ""
-            },
-            "require": {
-                "php": "^5.5.9|>=7.0.8",
-                "symfony/dom-crawler": "~2.8|~3.0"
-            },
-            "require-dev": {
-                "symfony/css-selector": "~2.8|~3.0",
-                "symfony/process": "~2.8|~3.0"
-            },
-            "suggest": {
-                "symfony/process": ""
-            },
-            "type": "library",
-            "extra": {
-                "branch-alias": {
-                    "dev-master": "3.3-dev"
-                }
-            },
-            "autoload": {
-                "psr-4": {
-                    "Symfony\\Component\\BrowserKit\\": ""
-                },
-                "exclude-from-classmap": [
-                    "/Tests/"
-                ]
-            },
-            "notification-url": "https://packagist.org/downloads/",
-            "license": [
-                "MIT"
-            ],
-            "authors": [
-                {
-                    "name": "Fabien Potencier",
-                    "email": "fabien@symfony.com"
-                },
-                {
-                    "name": "Symfony Community",
-                    "homepage": "https://symfony.com/contributors"
-                }
-            ],
-            "description": "Symfony BrowserKit Component",
-            "homepage": "https://symfony.com",
-            "time": "2017-07-29T21:54:42+00:00"
-        },
         {
             "name": "symfony/cache",
             "version": "v3.3.9",
@@ -2076,59 +2019,6 @@
             "homepage": "https://symfony.com",
             "time": "2017-09-06T16:40:18+00:00"
         },
-        {
-            "name": "symfony/css-selector",
-            "version": "v3.3.9",
-            "source": {
-                "type": "git",
-                "url": "https://github.com/symfony/css-selector.git",
-                "reference": "c5f5263ed231f164c58368efbce959137c7d9488"
-            },
-            "dist": {
-                "type": "zip",
-                "url": "https://api.github.com/repos/symfony/css-selector/zipball/c5f5263ed231f164c58368efbce959137c7d9488",
-                "reference": "c5f5263ed231f164c58368efbce959137c7d9488",
-                "shasum": ""
-            },
-            "require": {
-                "php": "^5.5.9|>=7.0.8"
-            },
-            "type": "library",
-            "extra": {
-                "branch-alias": {
-                    "dev-master": "3.3-dev"
-                }
-            },
-            "autoload": {
-                "psr-4": {
-                    "Symfony\\Component\\CssSelector\\": ""
-                },
-                "exclude-from-classmap": [
-                    "/Tests/"
-                ]
-            },
-            "notification-url": "https://packagist.org/downloads/",
-            "license": [
-                "MIT"
-            ],
-            "authors": [
-                {
-                    "name": "Jean-François Simon",
-                    "email": "jeanfrancois.simon@sensiolabs.com"
-                },
-                {
-                    "name": "Fabien Potencier",
-                    "email": "fabien@symfony.com"
-                },
-                {
-                    "name": "Symfony Community",
-                    "homepage": "https://symfony.com/contributors"
-                }
-            ],
-            "description": "Symfony CssSelector Component",
-            "homepage": "https://symfony.com",
-            "time": "2017-07-29T21:54:42+00:00"
-        },
         {
             "name": "symfony/debug",
             "version": "v3.3.9",
@@ -2334,62 +2224,6 @@
             "homepage": "https://symfony.com",
             "time": "2017-09-11T15:55:22+00:00"
         },
-        {
-            "name": "symfony/dom-crawler",
-            "version": "v3.3.9",
-            "source": {
-                "type": "git",
-                "url": "https://github.com/symfony/dom-crawler.git",
-                "reference": "6b511d7329b203a620f09a2288818d27dcc915ae"
-            },
-            "dist": {
-                "type": "zip",
-                "url": "https://api.github.com/repos/symfony/dom-crawler/zipball/6b511d7329b203a620f09a2288818d27dcc915ae",
-                "reference": "6b511d7329b203a620f09a2288818d27dcc915ae",
-                "shasum": ""
-            },
-            "require": {
-                "php": "^5.5.9|>=7.0.8",
-                "symfony/polyfill-mbstring": "~1.0"
-            },
-            "require-dev": {
-                "symfony/css-selector": "~2.8|~3.0"
-            },
-            "suggest": {
-                "symfony/css-selector": ""
-            },
-            "type": "library",
-            "extra": {
-                "branch-alias": {
-                    "dev-master": "3.3-dev"
-                }
-            },
-            "autoload": {
-                "psr-4": {
-                    "Symfony\\Component\\DomCrawler\\": ""
-                },
-                "exclude-from-classmap": [
-                    "/Tests/"
-                ]
-            },
-            "notification-url": "https://packagist.org/downloads/",
-            "license": [
-                "MIT"
-            ],
-            "authors": [
-                {
-                    "name": "Fabien Potencier",
-                    "email": "fabien@symfony.com"
-                },
-                {
-                    "name": "Symfony Community",
-                    "homepage": "https://symfony.com/contributors"
-                }
-            ],
-            "description": "Symfony DomCrawler Component",
-            "homepage": "https://symfony.com",
-            "time": "2017-09-11T15:55:22+00:00"
-        },
         {
             "name": "symfony/event-dispatcher",
             "version": "v3.3.9",
@@ -4898,6 +4732,116 @@
             ],
             "time": "2017-05-22T07:24:03+00:00"
         },
+        {
+            "name": "symfony/browser-kit",
+            "version": "v3.3.9",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/browser-kit.git",
+                "reference": "aee7120b058c268363e606ff5fe8271da849a1b5"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/browser-kit/zipball/aee7120b058c268363e606ff5fe8271da849a1b5",
+                "reference": "aee7120b058c268363e606ff5fe8271da849a1b5",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^5.5.9|>=7.0.8",
+                "symfony/dom-crawler": "~2.8|~3.0"
+            },
+            "require-dev": {
+                "symfony/css-selector": "~2.8|~3.0",
+                "symfony/process": "~2.8|~3.0"
+            },
+            "suggest": {
+                "symfony/process": ""
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "3.3-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Symfony\\Component\\BrowserKit\\": ""
+                },
+                "exclude-from-classmap": [
+                    "/Tests/"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Fabien Potencier",
+                    "email": "fabien@symfony.com"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Symfony BrowserKit Component",
+            "homepage": "https://symfony.com",
+            "time": "2017-07-29T21:54:42+00:00"
+        },
+        {
+            "name": "symfony/css-selector",
+            "version": "v3.3.9",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/css-selector.git",
+                "reference": "c5f5263ed231f164c58368efbce959137c7d9488"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/css-selector/zipball/c5f5263ed231f164c58368efbce959137c7d9488",
+                "reference": "c5f5263ed231f164c58368efbce959137c7d9488",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^5.5.9|>=7.0.8"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "3.3-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Symfony\\Component\\CssSelector\\": ""
+                },
+                "exclude-from-classmap": [
+                    "/Tests/"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Jean-François Simon",
+                    "email": "jeanfrancois.simon@sensiolabs.com"
+                },
+                {
+                    "name": "Fabien Potencier",
+                    "email": "fabien@symfony.com"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Symfony CssSelector Component",
+            "homepage": "https://symfony.com",
+            "time": "2017-07-29T21:54:42+00:00"
+        },
         {
             "name": "symfony/debug-bundle",
             "version": "v3.3.9",
@@ -4960,6 +4904,62 @@
             "homepage": "https://symfony.com",
             "time": "2017-08-10T07:07:06+00:00"
         },
+        {
+            "name": "symfony/dom-crawler",
+            "version": "v3.3.9",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/dom-crawler.git",
+                "reference": "6b511d7329b203a620f09a2288818d27dcc915ae"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/dom-crawler/zipball/6b511d7329b203a620f09a2288818d27dcc915ae",
+                "reference": "6b511d7329b203a620f09a2288818d27dcc915ae",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^5.5.9|>=7.0.8",
+                "symfony/polyfill-mbstring": "~1.0"
+            },
+            "require-dev": {
+                "symfony/css-selector": "~2.8|~3.0"
+            },
+            "suggest": {
+                "symfony/css-selector": ""
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "3.3-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Symfony\\Component\\DomCrawler\\": ""
+                },
+                "exclude-from-classmap": [
+                    "/Tests/"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Fabien Potencier",
+                    "email": "fabien@symfony.com"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Symfony DomCrawler Component",
+            "homepage": "https://symfony.com",
+            "time": "2017-09-11T15:55:22+00:00"
+        },
         {
             "name": "symfony/dotenv",
             "version": "v3.3.9",