Update ruby version requirement to allow ruby 3.0

[andrewsheelan]

Ruby 3.0.0 #121

[jejacks0n]

I'll try to cut a release of this by the weekend.

[jmziya]

Hey @jejacks0n , a release for this would be great. Without the release it's conflicting with #115 somehow, if you specify in Gemfile to pull from this github repo.

[andrewsheelan]

Not the best solution, I had add this along for now with ruby 3 upgrade. This monkey patch helped:
config/initializers/apitome.rb

Rails.configuration.to_prepare do
  Apitome::DocsController.class_eval do
    def open(file, file_opts)
      URI.open(file, **file_opts)
    end
  end
end