fix kernel root, linux dir separator on windows, to fix cache:clear issue

src/Symfony/Component/HttpKernel/Kernel.php

@@ -374,7 +374,7 @@ abstract class Kernel implements KernelInterface
     {
         if (null === $this->rootDir) {
             $r = new \ReflectionObject($this);
-            $this->rootDir = dirname($r->getFileName());
+            $this->rootDir = str_replace('\\', '/', dirname($r->getFileName()));
         }
 
         return $this->rootDir;