Don't use deprecated success? predicate

See rspec/rspec-rails#2014 for details, fixes errors like

     Failure/Error: expect(response).to be_success
       expected #<ActionDispatch::TestResponse:0x0000560db29e9880 @mon_mutex=#<Thread::Mutex:0x0000560db29e9808>, @mo...ders:0x0000560db2cdf170 @Req=#<ActionController::TestRequest:0x0000560db29ea370 ...>>, @variant=[]>> to respond to `success?`
     # ./spec/controllers/people_controller_spec.rb:37:in `block (3 levels) in <main>'
     # ./spec/support/database_cleaner.rb:13:in `block (3 levels) in <main>'
     # ./spec/support/database_cleaner.rb:12:in `block (2 levels) in <main>'

lib/templates/rspec/scaffold/controller_spec.rb

@@ -21,7 +21,7 @@
     it "returns a success response" do
       <%= class_name %>.create! valid_attributes
       get :index, :params => {}, :session => valid_session
-      expect(response).to be_success
+      expect(response).to be_successful
     end
   end
 
@@ -32,14 +32,14 @@
       get :show,
         :params => {:id => <%= file_name %>.to_param},
         :session => valid_session
-      expect(response).to be_success
+      expect(response).to be_successful
     end
   end
 
   describe "GET #new" do
     it "returns a success response" do
       get :new, :params => {}, :session => valid_session
-      expect(response).to be_success
+      expect(response).to be_successful
     end
   end
 
@@ -49,7 +49,7 @@
       get :edit,
         :params => {:id => <%= file_name %>.to_param},
         :session => valid_session
-      expect(response).to be_success
+      expect(response).to be_successful
     end
   end
 
@@ -76,7 +76,7 @@
         post :create,
           :params => {:<%= ns_file_name %> => invalid_attributes},
           :session => valid_session
-        expect(response).to be_success
+        expect(response).to be_successful
       end
     end
   end
@@ -120,7 +120,7 @@
             :<%= ns_file_name %> => invalid_attributes
           },
           :session => valid_session
-        expect(response).to be_success
+        expect(response).to be_successful
       end
     end
   end