minor symfony#5191 Fixed inconsistency (jperovic)

This PR was submitted for the 2.6 branch but it was merged into the 2.3 branch instead (closes symfony#5191).

Discussion
----------

Fixed inconsistency

All examples but "Annotation" use parameter named  "username" whereas it uses parameter "name".

Commits
-------

3c9e738 Fixed inconsistency

Author: wouterj

cookbook/routing/slash_in_parameter.rst

@@ -31,9 +31,9 @@ a more permissive regex path.
         class DemoController
         {
             /**
-             * @Route("/hello/{name}", name="_hello", requirements={"name"=".+"})
+             * @Route("/hello/{username}", name="_hello", requirements={"username"=".+"})
              */
-            public function helloAction($name)
+            public function helloAction($username)
             {
                 // ...
             }