Add Ruby 2.0.0

Fixes #181

Add cache-version input

• See #175
• Fixes #174

Fix download URLs for Ruby < 2.4 on Windows

• See #172

Add TruffleRuby 21.1.0

v1.70.0

Add TruffleRuby 21.1.0

Add RubyInstaller 2.5.9, 2.6.7, 2.7.3 and 3.0.1 builds

v1.69.0

Add reminder to use ruby/setup-ruby@v1 for latest Ruby releases

Add Ruby 2.5.9, 2.6.7, 2.7.3 and 3.0.1

Automatically pick the latest version of 2.6 for testing

* 2.6.7 is not yet available on Windows

Add JRuby 9.2.17.0

• #165

JRuby 9.3+ ships with Bundler 2

v1.66.1

Document the logic for whether to install Bundler

Add JRuby 9.2.16.0

v1.66.0

Add JRuby 9.2.16.0

Add JRuby 9.2.15.0

v1.65.0

Add JRuby 9.2.15.0