run 'mkdir' only if the directory doesn't exist yet (#481)

* run 'mkdir' only if the directory doesn't exist yet

* codestyle

* Use 'id_dir' instead of 'file_exists'

Co-authored-by: Francescu Garoby <francescu.garoby@docndoc.fr>

Author: fgaroby

.php-cs-fixer.dist.php

@@ -13,7 +13,10 @@
 
 $config = new PhpCsFixer\Config('faker');
 
-mkdir('.build/php-cs-fixer', 0755, true);
+if (!is_dir('.build/php-cs-fixer')) {
+    mkdir('.build/php-cs-fixer', 0755, true);
+}
+
 return $config
     ->setCacheFile('.build/php-cs-fixer/cache')
     ->setFinder($finder)