ruby2.devkit is broken due to bintray sunset

[jcaselman]

Relevant discussion: oneclick/rubyinstaller#400

The devkit installers are now hosted at https://github.com/oneclick/rubyinstaller/releases/tag/devkit-4.7.2

I've opened a PR to use the new URLs for the package #325

[larskanis]

This is fixed upstream, but you probably have to update the download link.