Use new Travis docker based env and caching

Author: wouterj

.travis.yml

@@ -5,6 +5,12 @@ php:
     - 5.5
     - 5.6
     - hhvm
+    
+sudo: false
+
+cache:
+    directories:
+        - $HOME/.composer/cache
 
 env:
   - SYMFONY_VERSION=2.5.*
@@ -25,7 +31,7 @@ matrix:
 
 before_script:
   - composer self-update
-  - composer require symfony/symfony:${SYMFONY_VERSION} --prefer-source
+  - composer require symfony/symfony:${SYMFONY_VERSION} --prefer-dist
   - vendor/symfony-cmf/testing/bin/travis/phpcr_odm_doctrine_dbal.sh
 
 script: