Added testing on more versions

This tests on PHP 5.6 and 5.6 and HHVM.
It also adds some builds with specific Symfony versions rather than the latest stable.

Author: stof

.travis.yml

@@ -3,10 +3,20 @@ language: php
 php:
     - 5.3
     - 5.4
+    - 5.5
+    - 5.6
+    - hhvm
+
+matrix:
+  include:
+    - php: 5.5
+      env: SYMFONY_VERSION='2.3.*'
+    - php: 5.5
+      env: SYMFONY_VERSION='2.5.*@dev'
 
 before_script:
-    - curl -s http://getcomposer.org/installer | php
-    - php composer.phar install --dev
+    - sh -c 'if [ "$SYMFONY_VERSION" != "" ]; then composer require --no-update symfony/symfony=$SYMFONY_VERSION; fi;'
+    - composer install --no-interaction --prefer-source
 
 notifications:
     email: