TASK: Add php linting

To make sure there are no syntax errors in files.

.travis.yml

@@ -0,0 +1,14 @@
+language: php
+
+php:
+  - 5.6
+  - 7.0
+  - 7.1
+  - 7.2
+
+install:
+  - composer install
+
+script:
+  - composer lint
+  - composer cgl

composer.json

@@ -20,6 +20,10 @@
     },
     "scripts": {
         "lint": [
+            "! find Classes -type f -name \"*.php\" -exec php -d error_reporting=32767 -l {} \\; 2>&1 >&- | grep \"^\"",
+            "! find Tests -type f -name \"*.php\" -exec php -d error_reporting=32767 -l {} \\; 2>&1 >&- | grep \"^\""
+        ],
+        "cgl": [
             "./vendor/bin/phpcs"
         ],
         "post-install-cmd": [