test different Symfony2 versions

.travis.yml

@@ -5,6 +5,19 @@ php:
     - 5.4
     - 5.5
 
+env:
+    - SYMFONY_VERSION=2.0.*
+    - SYMFONY_VERSION=2.1.*
+    - SYMFONY_VERSION=2.2.*
+    - SYMFONY_VERSION=2.3.*
+    - SYMFONY_VERSION=dev-master
+
 before_script:
-  - curl -s http://getcomposer.org/installer | php
-  - php composer.phar install --dev --prefer-source
+    - composer require symfony/symfony:${SYMFONY_VERSION} --no-interaction --prefer-source
+
+script:
+    - phpunit --coverage-text
+
+matrix:
+    allow_failures:
+        - env: SYMFONY_VERSION=dev-master