Update codeclimate configuration

[mvz]

I would like to achieve the following:

1. be able to run rubocop locally, preferally with the same version that codeclimate uses
2. update rubocop configuration so it won't try and fail to parse using Ruby 2.1 syntax in codeclimate

Codeclimate claims it uses rubocop 0.52.1 (https://docs.codeclimate.com/docs/rubocop), but that version gives errors with the current .rubocop.yml.

[mvz]

Unfortunately, it seems this branch won't be checked by codeclimate because it is not in the main repository.

[mvz]

@maartenvanvliet how do you feel about codeclimate and rubocop? If you're not using codeclimate, I'd suggest adding rubocop to the bundle and running it using github actions. That way, it's easier to run locally as well. I would also clean up the configuration.

[maartenvanvliet]

I think CodeClimate can be dropped altogether and rubocop can run in GH actions.