Associated Groups, Ruby 2.4.0 and more

* Add author name next to release notes in changelog (#8564) via Felix Krause
* Fix modifying of frozen strings via config files and tests (#8562) via Felix Krause
* Find and delete keychains with -db extension (#8511) via Fred Cox
* Ignore newline of demo user information (#8579) via Kohki Miki
* Update supply to promote version codes correctly (#8474) via Tom Wilson
* Fix error installing the AppleWWDRCA certificate on multiuser systems (#8509) via Fred Cox
* Add 'associated_groups' attribute to Spaceship::Portal::App (#8516) via yukiasai
* Revise action alias handling (#8565) via Fumiya Nakamura
* Add git_user_name and git_user_email option to match (#8550) via Kouki Saito
* Update fastlane tests to work with Ruby 2.4.0 (#8545) via Felix Krause
* Fix table formatting in README (#8547) via Jacob Bijani
* Update `gym build` description (#8541) via Felix Krause
* [produce] `app_version` option is ignored. (#8496) via yukiasai

https://github.com/fastlane/fastlane/releases/tag/2.21.0
