Fix UsernameNotFoundException example (take 2)

here is the fix properly applied to master

Author: Johnny Robeson

cookbook/security/entity_provider.rst

@@ -384,7 +384,7 @@ The code below shows the implementation of the
                 // if there is no record matching the criteria.
                 $user = $q->getSingleResult();
             } catch (NoResultException $e) {
-                throw new UsernameNotFoundException(sprintf('Unable to find an active admin AcmeUserBundle:User object identified by "%s".', $username), null, 0, $e);
+                throw new UsernameNotFoundException(sprintf('Unable to find an active admin AcmeUserBundle:User object identified by "%s".', $username), 0, $e);
             }
 
             return $user;