Update routing.rst

Author: Foksler

components/routing.rst

@@ -40,6 +40,7 @@ A routing system has three parts:
 Here is a quick example::
 
     use App\Controller\BlogController;
+    use Symfony\Component\Routing\Generator\UrlGenerator;
     use Symfony\Component\Routing\Matcher\UrlMatcher;
     use Symfony\Component\Routing\RequestContext;
     use Symfony\Component\Routing\Route;