Need to support JRuby installations

[keithrbennett]

In addition to the standard C Ruby implementation, I sometimes use JRuby.

Am I correct in understanding that rv does not yet support JRuby installations? If it does not, then this is a request to add that support.

Thanks for rv! I have high hopes for it, especially for rvx.

[indirect]

Today, you can install JRuby with ruby-install or ruby-build, and rv will support switching to JRuby. If you want to send us a PR to install JRuby, we would also love that. 😄