bug #3671 miss extends keyword in define BlogController class (ghanbari)

This PR was submitted for the 2.4 branch but it was merged into the 2.3 branch instead (closes #3671).

Discussion
----------

miss extends keyword in define BlogController class

Commits
-------

934b14f Update acl.rst

cookbook/security/acl.rst

@@ -108,7 +108,7 @@ Creating an ACL, and adding an ACE
     use Symfony\Component\Security\Acl\Domain\UserSecurityIdentity;
     use Symfony\Component\Security\Acl\Permission\MaskBuilder;
 
-    class BlogController
+    class BlogController extends Controller
     {
         // ...