Don't equate Rails with Ruby (some projects follow semver very closely).

Rails follows a shifted semver version, as documented here: https://github.com/rails/rails/blob/master/guides/source/mai...

Bumps from 4.x to 4.y might contain smaller breaking changes.

For a large project as Rails, I find that reasonable, otherwise, we'd be at Rails 20 by now, which also doesn't quite give a good sense of how the project evolved.