Try to get hhvm to work

Author: rikbruil

.travis.yml

@@ -1,13 +1,15 @@
 language: php
 
-php:
-  - 5.5
-  - 5.6
-  - 7.0
-  - 7.1
-  - hhvm
-
 matrix:
+  include:
+    - php: 5.5
+    - php: 5.6
+    - php: 7.0
+    - php: 7.1
+    - php: hhvm
+      sudo: required
+      dist: trusty
+      group: edge
   allow_failures:
     - php: 7.1
     - php: hhvm