minor #13830 Update access_denied_handler.rst (atailouloute)

This PR was merged into the 3.4 branch.

Discussion
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Update access_denied_handler.rst

Fix XML config.

Commits
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520bad3 Update access_denied_handler.rst

Author: javiereguiluz

security/access_denied_handler.rst

@@ -50,7 +50,7 @@ configure it under your firewall:
 
         <config>
             <firewall name="main">
-                <access_denied_handler>AppBundle\Security\AccessDeniedHandler</access_denied_handler>
+                <access-denied-handler>AppBundle\Security\AccessDeniedHandler</access-denied-handler>
             </firewall>
         </config>