don't build against HHVM any more, not supported anyway

Author: Frank Kleine

.travis.yml

@@ -13,13 +13,6 @@ matrix:
   include:
     - php: 5.3
       dist: precise
-    # test against the latest HHVM version by using a newer image
-    - php: hhvm
-      sudo: true
-      dist: trusty
-      group: edge # Use edge image until the next travis CI stable image update
-  allow_failures:
-    - php: hhvm
 
 install:
   - composer install