Simplify usage of dirname()

Author: fabpot

DeprecationErrorHandler/Deprecation.php

@@ -269,7 +269,7 @@ private static function getVendors()
             foreach (get_declared_classes() as $class) {
                 if ('C' === $class[0] && 0 === strpos($class, 'ComposerAutoloaderInit')) {
                     $r = new \ReflectionClass($class);
-                    $v = \dirname(\dirname($r->getFileName()));
+                    $v = \dirname($r->getFileName(), 2);
                     if (file_exists($v.'/composer/installed.json')) {
                         self::$vendors[] = $v;
                         $loader = require $v.'/autoload.php';