Merge pull request #6556 from Homebrew/ruby-2.6

.gitignore

Library/Homebrew/Gemfile

Library/Homebrew/Gemfile.lock

Library/Homebrew/brew.sh

Library/Homebrew/cmd/vendor-install.sh

Library/Homebrew/extend/os/mac/diagnostic.rb

Library/Homebrew/extend/string.rb

Library/Homebrew/test/cask/installer_spec.rb

Library/Homebrew/test/cmd/install_spec.rb

Library/Homebrew/test/cmd/migrate_spec.rb

Library/Homebrew/test/cmd/reinstall_spec.rb

Library/Homebrew/test/cmd/upgrade_spec.rb

Library/Homebrew/test/dev-cmd/ruby_spec.rb

Library/Homebrew/test/dev-cmd/test_spec.rb

Library/Homebrew/test/rubocops/formula_desc_spec.rb

Library/Homebrew/test/spec_helper.rb

Library/Homebrew/utils/ruby.sh

Library/Homebrew/vendor/bundle/bundler/setup.rb

.../bundle/ruby/2.3.0/gems/backports-3.15.0/lib/backports.rb

...0/gems/backports-3.15.0/lib/backports/2.4.0/comparable.rb