commented hhvm test on travis until bugs have been fixed

.travis.yml

@@ -3,7 +3,7 @@ language: php
 php:
   - 5.4
   - 5.5
-  - hhvm
+#  - hhvm # commented until composer or hhvm get fixed: https://github.com/facebook/hhvm/issues/1347
 
 services:
   - redis-server