JRuby and Jenkins

This was how to build a Jenkins plugin using JRuby, as featured here:

https://github.com/jenkinsci/jenkins.rb/wiki/Getting-Started-With-Ruby-Plugins

brew install jruby
brew install ruby193
jruby -S gem install bundler
jruby -S bundle install
jruby -S rake
jruby -S rake rspec
jruby -S gem install jpi
jruby -S jpi build

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