[Fabbot] Do not run php-cs-fixer if there are no change in src/

Author: lyrixx

.php_cs.dist

@@ -1,5 +1,9 @@
 <?php
 
+if (!file_exists(__DIR__.'/src')) {
+    exit(0);
+}
+
 return PhpCsFixer\Config::create()
     ->setRules(array(
         '@Symfony' => true,