Fix HHVM version (#352)

GrahamCampbell · web-flow · commit e57f2fc9c86b · 2019-03-06T09:38:31.000Z
diff --git a/.travis.yml b/.travis.yml
@@ -11,7 +11,7 @@ php:
   - 7.1
   - 7.2
   - 7.3
-  - hhvm
+  - hhvm-3.18
 
 install: travis_retry composer install --no-interaction --prefer-source
 
