minor #5644 Update page_creation.rst (jeromenadaud)

This PR was submitted for the 2.7 branch but it was merged into the 2.3 branch instead (closes #5644).

Discussion
----------

Update page_creation.rst

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.7
| Fixed tickets |

Commits
-------

1c8cfbe Update page_creation.rst

Author: wouterj

book/page_creation.rst

@@ -104,7 +104,7 @@ Just add a second method to ``LuckyController``::
     // src/AppBundle/Controller/LuckyController.php
     // ...
 
-    class LuckyController
+    class LuckyController extends Controller
     {
         // ...
 
@@ -137,7 +137,7 @@ You can even shorten this with the handy :class:`Symfony\\Component\\HttpFoundat
     // --> don't forget this new use statement
     use Symfony\Component\HttpFoundation\JsonResponse;
 
-    class LuckyController
+    class LuckyController extends Controller
     {
         // ...
 
@@ -170,7 +170,7 @@ at the end:
         // src/AppBundle/Controller/LuckyController.php
         // ...
 
-        class LuckyController
+        class LuckyController extends Controller
         {
             /**
              * @Route("/lucky/number/{count}")
@@ -224,7 +224,7 @@ The best part is that you can access this value and use it in your controller::
     // src/AppBundle/Controller/LuckyController.php
     // ...
 
-    class LuckyController
+    class LuckyController extends Controller
     {
 
         /**