Pull in changelog for Rails

[dependabot]

Pull in changelog for Rails

[greysteil]

Yeah, I'd really like to do this, but Rails doesn't keep a changelog for the master gem, only for the constituent parts. I might be able to persuade them to start doing GitHub releases, though - which would make things a lot better. Let me try...

[tijmenb]

Have you considered including the changelog of the transitive dependencies as well? If it worked like that, you'd get the changelogs for activemodel, actionview, etc. Could be a generic solution for this particular problem.

[greysteil]

Yeah, we don't add much detail of the sub-dependencies that get updated alongside the main one at the moment, but I'd be quite keen on doing so. The changes required to this repo would be to store the sub-dependencies that change in the UpdateChecker and then use those details in the PullRequestCreator class. (The alternative would be comparing diffs in the PullRequestCreator class to get the changed dependencies, but that wouldn't be language agnostic.)

[greysteil]

Closing in favour of #446. Good suggestion @tijmenb!