Correct MockController usage

Author: madeindjs

rails6/en/chapter04-athentification.adoc

@@ -376,7 +376,7 @@ Then we can implement our two tests right after
 class AuthenticableTest < ActionDispatch::IntegrationTest
   setup do
     @user = users(:one)
-    @authentication = Authentication.new
+    @authentication = MockController.new
   end
 
   test 'should get user from Authorization token' do