Update .travis.yml

Author: sascha432

.travis.yml

@@ -1,3 +1,4 @@
+dist: trusty
 language: php
 php:
   - '5.6'
@@ -13,4 +14,4 @@ script:
   - vendor/bin/phpunit --verbose
 
 matrix:
-  fast_finish: true
+  fast_finish: true