Add support for ruby 3.0 & 3.1

[philip-maina]

Summary

This adds support for Ruby 3.0 and 3.1. It builds off of this pull request.

Highlights

1. Fixes separation of positional arguments from keyword arguments in ActsAsHashids::Core::ClassMethods#has_many

2. Upgrades rubocop to ~> 0.81.0. This was necessitated by two things.

   • Ruby 3.1 ships with psych 4.0 by default whose #safe_load method now accepts both positional and keyword arguments. This results in an ArgumentError when calling Rubocop::ConfigLoader.yaml_safe_load.
   • Calling Rubocop::ConfigLoaderResolver#merge in Rubocop::ConfigLoaderResolver#merge_with_default results in an ArgumentError because opts should now be passed as a keyword argument.

3. Upgrades the least required ruby version to 2.3.0 since this is the least required Ruby version by rubocop, '~> 0.81.0'.

[dtaniwaki]

Thank you!