Print the target ruby version derived by rubocop

rubocop-ruby.rake

namespace :rubocop do
  task :ruby do
    require "rubocop"

    config = RuboCop::ConfigStore.new.for_dir Dir.pwd
    target = RuboCop::TargetRuby.new(config)

    if Rake.application.options.trace || verbose == true
      rake_output_message "derived target ruby version (last wins):"
      rake_output_message target.class.const_get(:SOURCES).reverse.map { |s| s.new config }
        .map { |s| "#{s.version.inspect} set by #{s}" }
    end

    puts target.version
  end
end

Recent rubocops may also print this information in rubocop's -V version output: rubocop/rubocop#13311