Add support for jruby-head

• See MSP-Greg#1
• Use the automatic latest release asset link for head builds

Add support for .tool-versions

See #17.

Do not remove dev tools from PATH on Windows

Fixes #19.

Cleanup PATH for JRuby on Windows

• That way we remove the default Ruby in PATH which was confusing (#18).

Add support for Ruby 2.2

* Use Ruby 2.2.6 from RubyInstaller on Windows since there is no more
  recent release of Ruby 2.2.

This action was transferred to ruby/setup-ruby

Please replace

    - uses: eregon/use-ruby-action@v1

with:

    - uses: ruby/setup-ruby@v1

The old usage should still work thanks to GitHub redirections but it's recommended to update.

Fix "Insecure world writable dir" warnings

Fixes #16.

Follow ruby-install-builder => ruby-builder repository rename

v1.12.1

Rename generate script

Add support for ruby-head

See #15.

Add support for truffleruby-head

v1.11.0

Add support for truffleruby-head