diff --git a/.travis.yml b/.travis.yml
index c3e48427..838c2467 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -69,6 +69,7 @@ before_install:
   - travis_retry composer self-update
 
 install:
+  - if [[ $TRAVIS_PHP_VERSION =~ ^5.6 ]]; then travis_retry composer update $COMPOSER_ARGS phpunit/phpunit phpunit/phpunit-mock-objects phpunit/php-code-coverage ; fi
   - if [[ $TEST_COVERAGE == 'true' ]]; then travis_retry composer require --dev $COMPOSER_ARGS $COVERAGE_DEPS ; fi
   - if [[ $DEPS == 'latest' ]]; then travis_retry composer update $COMPOSER_ARGS ; fi
   - if [[ $DEPS == 'lowest' ]]; then travis_retry composer update --prefer-lowest --prefer-stable $COMPOSER_ARGS ; fi
diff --git a/composer.lock b/composer.lock
index ed34ac9e..1830fbc5 100644
--- a/composer.lock
+++ b/composer.lock
@@ -1059,40 +1059,39 @@
         },
         {
             "name": "phpunit/php-code-coverage",
-            "version": "4.0.4",
+            "version": "5.0.0",
             "source": {
                 "type": "git",
                 "url": "https://github.com/sebastianbergmann/php-code-coverage.git",
-                "reference": "c14196e64a78570034afd0b7a9f3757ba71c2a0a"
+                "reference": "e7d7a4acca58e45bdfd00221563d131cfb04ba96"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/sebastianbergmann/php-code-coverage/zipball/c14196e64a78570034afd0b7a9f3757ba71c2a0a",
-                "reference": "c14196e64a78570034afd0b7a9f3757ba71c2a0a",
+                "url": "https://api.github.com/repos/sebastianbergmann/php-code-coverage/zipball/e7d7a4acca58e45bdfd00221563d131cfb04ba96",
+                "reference": "e7d7a4acca58e45bdfd00221563d131cfb04ba96",
                 "shasum": ""
             },
             "require": {
-                "php": "^5.6 || ^7.0",
-                "phpunit/php-file-iterator": "~1.3",
-                "phpunit/php-text-template": "~1.2",
+                "php": "^7.0",
+                "phpunit/php-file-iterator": "^1.3",
+                "phpunit/php-text-template": "^1.2",
                 "phpunit/php-token-stream": "^1.4.2",
-                "sebastian/code-unit-reverse-lookup": "~1.0",
-                "sebastian/environment": "^1.3.2 || ^2.0",
-                "sebastian/version": "~1.0|~2.0"
+                "sebastian/code-unit-reverse-lookup": "^1.0",
+                "sebastian/environment": "^2.0",
+                "sebastian/version": "^2.0"
             },
             "require-dev": {
-                "ext-xdebug": ">=2.1.4",
-                "phpunit/phpunit": "^5.4"
+                "ext-xdebug": "^2.5",
+                "phpunit/phpunit": "^6.0"
             },
             "suggest": {
                 "ext-dom": "*",
-                "ext-xdebug": ">=2.4.0",
                 "ext-xmlwriter": "*"
             },
             "type": "library",
             "extra": {
                 "branch-alias": {
-                    "dev-master": "4.0.x-dev"
+                    "dev-master": "5.0.x-dev"
                 }
             },
             "autoload": {
@@ -1118,7 +1117,7 @@
                 "testing",
                 "xunit"
             ],
-            "time": "2016-12-20 15:22:42"
+            "time": "2017-02-02 10:35:41"
         },
         {
             "name": "phpunit/php-file-iterator",
@@ -1303,16 +1302,16 @@
         },
         {
             "name": "phpunit/phpunit",
-            "version": "5.7.13",
+            "version": "6.0.6",
             "source": {
                 "type": "git",
                 "url": "https://github.com/sebastianbergmann/phpunit.git",
-                "reference": "60ebeed87a35ea46fd7f7d8029df2d6f013ebb34"
+                "reference": "e702506af102d0dc5312dd24b8e97fd6e58ce3ba"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/sebastianbergmann/phpunit/zipball/60ebeed87a35ea46fd7f7d8029df2d6f013ebb34",
-                "reference": "60ebeed87a35ea46fd7f7d8029df2d6f013ebb34",
+                "url": "https://api.github.com/repos/sebastianbergmann/phpunit/zipball/e702506af102d0dc5312dd24b8e97fd6e58ce3ba",
+                "reference": "e702506af102d0dc5312dd24b8e97fd6e58ce3ba",
                 "shasum": ""
             },
             "require": {
@@ -1321,33 +1320,33 @@
                 "ext-libxml": "*",
                 "ext-mbstring": "*",
                 "ext-xml": "*",
-                "myclabs/deep-copy": "~1.3",
-                "php": "^5.6 || ^7.0",
+                "myclabs/deep-copy": "^1.3",
+                "php": "^7.0",
                 "phpspec/prophecy": "^1.6.2",
-                "phpunit/php-code-coverage": "^4.0.4",
-                "phpunit/php-file-iterator": "~1.4",
-                "phpunit/php-text-template": "~1.2",
+                "phpunit/php-code-coverage": "^5.0",
+                "phpunit/php-file-iterator": "^1.4",
+                "phpunit/php-text-template": "^1.2",
                 "phpunit/php-timer": "^1.0.6",
-                "phpunit/phpunit-mock-objects": "^3.2",
+                "phpunit/phpunit-mock-objects": "^4.0",
                 "sebastian/comparator": "^1.2.4",
-                "sebastian/diff": "~1.2",
-                "sebastian/environment": "^1.3.4 || ^2.0",
-                "sebastian/exporter": "~2.0",
+                "sebastian/diff": "^1.2",
+                "sebastian/environment": "^2.0",
+                "sebastian/exporter": "^2.0",
                 "sebastian/global-state": "^1.1",
-                "sebastian/object-enumerator": "~2.0",
-                "sebastian/resource-operations": "~1.0",
-                "sebastian/version": "~1.0|~2.0",
-                "symfony/yaml": "~2.1|~3.0"
+                "sebastian/object-enumerator": "^2.0",
+                "sebastian/resource-operations": "^1.0",
+                "sebastian/version": "^2.0"
             },
             "conflict": {
-                "phpdocumentor/reflection-docblock": "3.0.2"
+                "phpdocumentor/reflection-docblock": "3.0.2",
+                "phpunit/dbunit": "<3.0"
             },
             "require-dev": {
                 "ext-pdo": "*"
             },
             "suggest": {
                 "ext-xdebug": "*",
-                "phpunit/php-invoker": "~1.1"
+                "phpunit/php-invoker": "^1.1"
             },
             "bin": [
                 "phpunit"
@@ -1355,7 +1354,7 @@
             "type": "library",
             "extra": {
                 "branch-alias": {
-                    "dev-master": "5.7.x-dev"
+                    "dev-master": "6.0.x-dev"
                 }
             },
             "autoload": {
@@ -1381,33 +1380,33 @@
                 "testing",
                 "xunit"
             ],
-            "time": "2017-02-10 09:05:10"
+            "time": "2017-02-08 05:57:26"
         },
         {
             "name": "phpunit/phpunit-mock-objects",
-            "version": "3.4.1",
+            "version": "4.0.0",
             "source": {
                 "type": "git",
                 "url": "https://github.com/sebastianbergmann/phpunit-mock-objects.git",
-                "reference": "45026c8383187ad1dcb14fbfec77dced265b9cfc"
+                "reference": "3819745c44f3aff9518fd655f320c4535d541af7"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/sebastianbergmann/phpunit-mock-objects/zipball/45026c8383187ad1dcb14fbfec77dced265b9cfc",
-                "reference": "45026c8383187ad1dcb14fbfec77dced265b9cfc",
+                "url": "https://api.github.com/repos/sebastianbergmann/phpunit-mock-objects/zipball/3819745c44f3aff9518fd655f320c4535d541af7",
+                "reference": "3819745c44f3aff9518fd655f320c4535d541af7",
                 "shasum": ""
             },
             "require": {
                 "doctrine/instantiator": "^1.0.2",
-                "php": "^5.6 || ^7.0",
+                "php": "^7.0",
                 "phpunit/php-text-template": "^1.2",
-                "sebastian/exporter": "^1.2 || ^2.0"
+                "sebastian/exporter": "^2.0"
             },
             "conflict": {
-                "phpunit/phpunit": "<5.4.0"
+                "phpunit/phpunit": "<6.0"
             },
             "require-dev": {
-                "phpunit/phpunit": "^5.4"
+                "phpunit/phpunit": "^6.0"
             },
             "suggest": {
                 "ext-soap": "*"
@@ -1415,7 +1414,7 @@
             "type": "library",
             "extra": {
                 "branch-alias": {
-                    "dev-master": "3.2.x-dev"
+                    "dev-master": "4.0.x-dev"
                 }
             },
             "autoload": {
@@ -1440,7 +1439,7 @@
                 "mock",
                 "xunit"
             ],
-            "time": "2016-11-19 09:07:46"
+            "time": "2017-02-02 10:36:38"
         },
         {
             "name": "psr/log",