Specify PHP 7.* versions to integrate against

Two years ago we didn't have PHP 7.2, which was just out a few days ago.

Defines `precise` version for testing PHP 5.3 as it is the only one that
supports that PHP version on Travis.

Author: augustohp

.travis.yml

@@ -1,15 +1,16 @@
-sudo:
-  false
+sudo: false
+language: php
 
-language:
-  php
-
-php:
-  - 5.3
-  - 5.4
-  - 5.5
-  - 5.6
-  - 7
+matrix:
+  include:
+    - php: 5.3
+      dist: precise
+    - php: 5.4
+    - php: 5.5
+    - php: 5.6
+    - php: 7.0
+    - php: 7.1
+    - php: 7.2
 
 cache:
   directories: