testing against php 5.6 and 7.2

Author: nicolasmure

.travis.yml

@@ -1,8 +1,10 @@
 language: php
 php:
     - '5.4'
+    - '5.6'
     - '7.0'
     - '7.1'
+    - '7.2'
 
 before_install:
     - mkdir -p build/logs