Update to Rails 6.0.2.2

This is a follow-up to the Rack v2.0.9 update. These changes should not affect GitLab because we use the redis-store gem for storing cookies instead of the built-in options (e.g. CacheStore, MemCacheStore, etc.). We also don't use rails/ujs yet. Full list of changes in Rails:

https://github.com/rails/rails/compare/v6.0.2..v6.0.2.2