Use new Travis docker based env and caching

Author: wouterj

.travis.yml

@@ -7,6 +7,12 @@ php:
     - 5.6
     - hhvm
 
+sudo: false
+
+cache:
+  directories:
+    - $HOME/.composer/cache
+
 env:
   - SYMFONY_VERSION=2.5.*
 
@@ -21,7 +27,7 @@ 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: phpunit --coverage-text