test different Symfony2 versions

.travis.yml

@@ -1,10 +1,23 @@
 language: php
 
 php:
-  - 5.3
-  - 5.4
-  - 5.5
+    - 5.3
+    - 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