Snapshot of Rails v6.0 as of 2020/12/12

詳細: ガイドのソースを6.0時点のものに更新 #938

* 引用元タグ: v6.0.0
* 引用元コミット: 66cabeda2c
* gitlocalize_jpブランチにソースを取り込んだ時のコミット: 330f2e7

cf. #938

Just finish updating Guieds: Rails 5.1 -> 5.2

Snapshot of Rails v5.1 before merging v5.2 PRs

Retroactively tagging version based on https://idobata.io/en/archives…

…/organization/yasslab/room/railsguides-news/2018-07-21#message_27512263 before where 5.1 update commit was merged

Update original guides up to master's 108a407:

- Merge pull request #25792 from prathamesh-sonpatki/test-typo
- rails/rails@108a407

tagging 3.2.2