add explicit php version in travis.yml

Pavlos Ratis · Pavlos Ratis · commit 9c22c7819097 · 2015-11-11T12:28:52.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -2,7 +2,7 @@ sudo: required
 dist: trusty
 language: php
 php:
-  - 5.5
+  - 5.5.9
 
 before_install:
   - sudo apt-get update
