ref: #515

It should be useful to create a nightly release so that users can use latest release without building reviewdog from the source.
Users can use new features before the new release and we can get feedback early.

I don't want to mess up the reviewdog release page with every nightly release nor don't want to delete and create release every day to keep the record, so I think we can create a different repository (e.g. reviewdog/nightly) and release nightly binary to there.

I found that atom seems to do the similar things.
https://blog.atom.io/2019/06/21/introducing-atom-nightly-releases.html
https://github.com/atom/atom-nightly-releases