fix mapping spec

spec/controllers/mappings_controller_spec.rb

@@ -24,6 +24,7 @@ RSpec.describe MappingsController, type: :controller do
         post :create, params: {
           mapping: valid_attributes
         }
+        mapping.updated_by = controller.current_user
         expect(comparable(Mapping.last)).to eq comparable(mapping)
       end
     end

spec/factories/mappings.rb

@@ -5,6 +5,7 @@ FactoryGirl.define do
     yloc 0
     map
     user
+    association :updated_by, factory: :user
     association :mappable, factory: :topic
 
     factory :mapping_random_location do