Fix build failures for php versions

Author: mebjas

.travis.yml

@@ -18,6 +18,8 @@ matrix:
 
 os:
   - linux
+  
+dist: trusty
 
 install:
   # Install composer packages, will also trigger dump-autoload
@@ -45,4 +47,4 @@ after_success:
 cache:
   directories:
   - vendor
-  - $HOME/.cache/composer
+  - $HOME/.cache/composer