Remove php 5.6 support from travis

.travis.yml

@@ -7,9 +7,9 @@ services:
 sudo: required
 
 php:
-  - 5.6
   - 7.0
   - 7.1
+  - 7.2
 
 env:
   - BASE_URL="http://127.0.0.1:8080"