Introduce PHP CS Fixer

.php_cs.dist

@@ -0,0 +1,11 @@
+<?php
+
+return PhpCsFixer\Config::create()
+    ->setRules([
+        'native_function_invocation' => null,
+    ])
+    ->setFinder(
+        PhpCsFixer\Finder::create()
+        ->in(__DIR__)
+    )
+;

.travis.yml

@@ -12,9 +12,12 @@ php:
 cache:
   directories:
     - $HOME/.composer/cache
+    - build/cache
 
 install:
   - composer install --prefer-dist
+  - mkdir -p build/cache
 
 script:
   - php vendor/bin/phpunit
+  - vendor/bin/php-cs-fixer --cache-file=build/cache/.php_cs.cache --diff --dry-run --stop-on-violation --verbose fix

composer.json

@@ -36,7 +36,8 @@
         "pear/pear-core-minimal": "^1.10"
     },
     "require-dev": {
-        "phpunit/phpunit": "<6.0"
+        "phpunit/phpunit": "<6.0",
+        "friendsofphp/php-cs-fixer": "^2.16"
     },
     "autoload": {
         "psr-0": {