Update travis.yml to support testing to PHP 7.2

Author: gmponos

.travis.yml

@@ -3,6 +3,7 @@ language: php
 sudo: false
 
 php:
+  - 7.2
   - 7.1
   - 7.0
   - 5.6
@@ -34,6 +35,8 @@ matrix:
       env: SYMFONY_VERSION=3.0.*
     - php: 7.1
       env: DEPENDENCIES=beta
+    - php: 7.2
+      env: DEPENDENCIES=beta
 
   allow_failures:
     - php: nightly