Loosen runtime Rubocop version

Allows gitlab-styles Gem users to use 0.92.x (0.92.0), 0.93.x (0.93.0 and 0.93.1), and upcoming 0.94.x etc. while ~> 0.91.1 allowed them to use only 0.91.x.

What problems to resolve

rubocop 0.91.1 supports only 2.8 (as well as 2.7 and earlier) as TargetRubyVersion config. This can be a critical blocker to upgrade Ruby to 3.0 in a project which uses gitlab-style Gem as long as it uses v6.0.0.

e.g., MR: gitlab-org/quality/toolbox!62 (merged) (job: https://gitlab.com/gitlab-org/quality/toolbox/-/jobs/1051604714)

Resources

• Changes on the upstream for supporting Ruby 3.0: https://github.com/rubocop/rubocop/pull/8785

Relates #12 (closed)