Fix a typo in deprecation warning. #process takes method instead of http_method.

actionpack/lib/action_controller/test_case.rb

@@ -755,7 +755,7 @@ def non_kwarg_request_warning
           Examples:
 
           get :show, params: { id: 1 }, session: { user_id: 1 }
-          process :update, http_method: :post, params: { id: 1 }
+          process :update, method: :post, params: { id: 1 }
         MSG
       end