Fix warning about content/media type for Rails 6

spec/controllers/matches_controller_spec.rb

@@ -49,7 +49,7 @@ RSpec.describe MatchesController, type: :controller do
     it 'should return success' do
       get :show, params: { id: @match.to_param }
       expect(response).to be_successful
-      expect(response.content_type).to eq('application/json')
+      expect(response.media_type).to eq('application/json')
     end
 
     it 'should return the correct state' do

spec/controllers/tournaments_controller_spec.rb

@@ -248,7 +248,7 @@ RSpec.describe TournamentsController, type: :controller do
         it 'renders a JSON response with the new tournament' do
           post :create, params: create_playoff_tournament_data
           expect(response).to have_http_status(:created)
-          expect(response.content_type).to eq('application/json')
+          expect(response.media_type).to eq('application/json')
           expect(response.location).to eq(tournament_url(Tournament.last))
         end
       end
@@ -329,7 +329,7 @@ RSpec.describe TournamentsController, type: :controller do
         it 'renders a JSON response with the tournament' do
           put :update, params: { id: @tournament.to_param }.merge(valid_update)
           expect(response).to have_http_status(:ok)
-          expect(response.content_type).to eq('application/json')
+          expect(response.media_type).to eq('application/json')
         end
 
         context 'any variable relevant for group stage to playoff transition changed' do