Add tests matrix

.travis.yml

@@ -1,14 +1,48 @@
 language: php
+
 php:
-  - 5.6
-  - 5.5
-  - 5.4
   - 5.3
+  - 5.4
+  - 5.5
+  - 5.6
   - 7.0
   - hhvm
 
 # This triggers builds to run on the new TravisCI infrastructure.
 # See: http://docs.travis-ci.com/user/workers/container-based-infrastructure/
 sudo: false
 
-install: travis_retry composer install --no-interaction --prefer-source
+matrix:
+  fast_finish: true
+  include:
+    - php: 5.3
+      env: polyfill='true'
+    - php: 5.3
+      env: polyfill='false'
+    - php: 5.4
+      env: polyfill='true'
+    - php: 5.4
+      env: polyfill='false'
+    - php: 5.5
+      env: polyfill='true'
+    - php: 5.5
+      env: polyfill='false'
+    - php: 5.6
+      env: polyfill='true'
+    - php: 5.6
+      env: polyfill='false'
+    - php: 7.0
+      env: polyfill='true'
+    - php: 7.0
+      env: polyfill='false'
+
+install: travis_retry composer install --no-interaction --prefer-source
+
+before_script:
+  - travis_retry composer self-update
+  - travis_retry composer install --no-interaction --prefer-source
+  - if [[ $polyfill = 'false' ]]; then travis_retry composer remove symfony/polyfill-mbstring; fi
+
+script:
+  - vendor/bin/phpunit
+

composer.json

@@ -15,8 +15,7 @@
         }
     ],
     "require": {
-        "php": ">=5.3.0",
-        "symfony/polyfill-mbstring": "~1.0"
+        "php": ">=5.3.0"
     },
     "require-dev": {
         "phpunit/phpunit": "~4.0"