Update Ruby/Jruby versions

[reshmabidikar]

Currently, the kpm_ci job fails. This needs to be fixed.

Some notes:

• There is a 3.x compatible version at https://github.com/Homebrew/homebrew-portable-ruby/releases. We need to try to upgrade to the 3.1.4 version (requires updating the rake file, the CI job, and making sure everything build/works fine).

• Finally, there is also a new JRuby version (9.4.5.0). See Rakefile. We should try to upgrade that too.