minor #4727 Renamed example: "Acme\BlogBundle" -> "AppBundle" (muxator)

This PR was merged into the 2.6 branch.

Discussion
----------

Renamed example: "Acme\BlogBundle" -> "AppBundle"

In the context of this sentence, the correct fully-qualified class name for the controller seems to be
  ```
  AppBundle\Controller\BlogController::showAction
  ```
and not
  ```
  Acme\BlogBundle\Controller\BlogController::showAction
  ```

Commits
-------

4c8d75f Renamed example: "Acme\BlogBundle" -> "AppBundle"

book/routing.rst

@@ -1169,7 +1169,7 @@ Notice that Symfony adds the string ``Controller`` to the class name (``Blog``
 => ``BlogController``) and ``Action`` to the method name (``show`` => ``showAction``).
 
 You could also refer to this controller using its fully-qualified class name
-and method: ``Acme\BlogBundle\Controller\BlogController::showAction``.
+and method: ``AppBundle\Controller\BlogController::showAction``.
 But if you follow some simple conventions, the logical name is more concise
 and allows more flexibility.