Enable pre-installed redis extension on travis

Author: snc

Diff for: .travis.yml

@@ -11,5 +11,7 @@ matrix:
     - php: hhvm
 
 before_script:
+  - echo "extension = redis.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
+  - phpenv rehash
   - composer install --dev
   - mkdir Snc && ln -s ../ Snc/RedisBundle