Fix parsing of ruby-version: ruby-3.0.0-preview1

Due to the two - it would trigger an issue in the logic due the unintuitive behavior of string.split(sep, limit) in JavaScript.

Only consider stable versions when using an engine-only version

• This only affected ruby-version: ruby.
• Fixes #110 (comment)

Add support for macos-11.0

• Fixes #94.

Always include the version in the platform

Also include the version in the platform for macos and windows

* Guess the platform based on $ImageOS.

Fix Bundler cache when there is no Gemfile.lock

• Fixes #105
• Also include the OS version in the cache key for Windows and macOS.

Always use Bundler 1 for JRuby 9.1.x

• Fixes #108

Use a hardcoded toolcache path since we need to extract there to let Ruby work

• Fixes #104 and #106.

truffleruby-head now ships with Bundler 2

v1.50.1

Bundler 2 is shipped with truffleruby-head now

Use the new builds under the hostedtoolcache

• See #98.
• Add support for Ruby 3.0.0-preview1 #100.
• Fix OpenSSL version used on macOS #97.

Remove Rubinius support

• Fixes #101.