Improve RuboCop rules (compatibility to Code Climate) (#3636)

https://github.com/codeclimate/codeclimate-rubocop/blob/08f8de84ebfb39caa96391e23816877278f6441c/Gemfile.lock#L38
Code Climate is using RuboCop v0.46.0.

Change several rules to maintain compatibility.

spec/models/user_spec.rb

@@ -150,7 +150,7 @@ RSpec.describe User, type: :model do
     end
 
     it 'saves cleared otp_backup_codes' do
-      user = Fabricate.build(:user, otp_backup_codes: %w[dummy dummy])
+      user = Fabricate.build(:user, otp_backup_codes: %w(dummy dummy))
       user.disable_two_factor!
       expect(user.reload.otp_backup_codes.empty?).to be true
     end