Disallow failures on HHVM on Travis

.travis.yml

@@ -8,10 +8,6 @@ php:
   - 5.6
   - hhvm
 
-matrix:
-  allow_failures:
-    - php: hhvm
-
 before_script:
     - sudo apt-get install parallel
     - rm -f ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/xdebug.ini