Tweak Travis CI config, because Laravel 5.3 doesn't support PHP 5.5

Author: tortuetorche

.travis.yml

@@ -9,6 +9,7 @@ php:
 matrix:
   allow_failures:
     - php: hhvm
+    - php: 5.5 # Laravel 5.3 doesn't support PHP 5.5
 
 sudo: false