Use the newer stack for HHVM on Tracis CI

Author: bocharsky-bw

.travis.yml

@@ -14,7 +14,11 @@ matrix:
     - php: 7.1
     - php: hhvm
   allow_failures:
-    - php: hhvm
+    # Use the newer stack for HHVM as HHVM does not support Precise anymore since a long time and so Precise has an outdated version
+    - php: hhvm-3.18
+      sudo: required
+      dist: trusty
+      group: edge
 
 before_install:
   - if [[ "$TRAVIS_PHP_VERSION" != "hhvm" ]]; then phpenv config-rm xdebug.ini; fi