Add PHP 7.0, 7.1 and 7.2 to travis.yml.

Author: tomzx

.travis.yml

@@ -1,9 +1,12 @@
 language: php
 php:
-  - 5.6
-  - 5.5
-  - 5.4
   - 5.3
+  - 5.4
+  - 5.5
+  - 5.6
+  - 7.0
+  - 7.1
+  - 7.2
   - hhvm
 install:
   - composer install --prefer-source --no-interaction