Add PHP 7.2 in not allowed failure

nightly is now 7.3.0-dev
also good bye HHVM

Author: j0k3r

.travis.yml

@@ -7,14 +7,13 @@ php:
     - 5.6
     - 7.0
     - 7.1
-    - hhvm
+    - 7.2
     - nightly
 
 # run build against nightly but allow them to fail
 matrix:
     fast_finish: true
     allow_failures:
-        - php: hhvm
         - php: nightly
 
 # faster builds on new travis setup not using sudo