Pin to stable dependencies

- Updated PHP to `^5.6 || ^7.0` (no more 5.5)
- Updated zend-mvc to 3.0 stable
  - Marked zend-mvc < 3.0.0 as a conflict

.travis.yml

@@ -25,24 +25,15 @@ env:
 matrix:
   fast_finish: true
   include:
-    - php: 5.5
-      env:
-        - DEPS=lowest
-    - php: 5.5
-      env:
-        - DEPS=locked
-        - DEPLOY_DOCS="$(if [[ $TRAVIS_BRANCH == 'master' && $TRAVIS_PULL_REQUEST == 'false' ]]; then echo -n 'true' ; else echo -n 'false' ; fi)"
-        - PATH="$HOME/.local/bin:$PATH"
-    - php: 5.5
-      env:
-        - DEPS=latest
     - php: 5.6
       env:
         - DEPS=lowest
     - php: 5.6
       env:
         - DEPS=locked
         - TEST_COVERAGE=true
+        - DEPLOY_DOCS="$(if [[ $TRAVIS_BRANCH == 'master' && $TRAVIS_PULL_REQUEST == 'false' ]]; then echo -n 'true' ; else echo -n 'false' ; fi)"
+        - PATH="$HOME/.local/bin:$PATH"
     - php: 5.6
       env:
         - DEPS=latest

composer.json

@@ -26,16 +26,19 @@
         }
     },
     "require": {
-        "php": "^5.5 || ^7.0",
+        "php": "^5.6 || ^7.0",
         "container-interop/container-interop": "^1.1",
-        "zendframework/zend-mvc": "dev-develop as 3.0.0 || ^3.0",
+        "zendframework/zend-mvc": "^3.0",
         "zendframework/zend-authentication": "^2.5.3",
         "zendframework/zend-servicemanager": "^2.7.5 || ^3.0.3"
     },
     "require-dev": {
         "phpunit/PHPUnit": "^4.5",
         "squizlabs/php_codesniffer": "^2.3.1"
     },
+    "conflict": {
+        "zendframework/zend-mvc": "< 3.0.0"
+    },
     "scripts": {
         "check": [
             "@cs-check",