Store the available Ruby versions in this repository

* That way it's always perfectly synchronized with the action. In
  practice querying another repository sometimes returned a stale copy.
* Avoids an extra HTTPS request.
* The axios dependency is no longer needed.
* Makes it possible to tweak the versions available according to the platform.

Author: eregon

README.md

@@ -34,8 +34,8 @@ Rubinius is only available on `ubuntu-latest`.
 
 The prebuilt rubies are generated by [eregon/ruby-install-builder](https://github.com/eregon/ruby-install-builder)
 and on Windows by [RubyInstaller2](https://github.com/oneclick/rubyinstaller2).  
-The full list of available Ruby versions can be seen at [versions.json](https://github.com/eregon/ruby-install-builder/blob/metadata/versions.json)
-for Ubuntu and macOS and at [windows-versions.js](https://github.com/eregon/use-ruby-action/blob/master/windows-versions.js) for Windows.
+The full list of available Ruby versions can be seen in [ruby-install-builder-versions.js](ruby-install-builder-versions.js)
+for Ubuntu and macOS and in [windows-versions.js](windows-versions.js) for Windows.
 
 ## Usage