I'm not sure that this will ever be a fair statistic because coffeescript should never really be used for shared / module code IMO. I love CS for my application code but would never release a package on github in CS, only JS.
Once you are releasing things outside of your controlled/team environment using anything but JS is just a loop for others to jump through.
I imagine a lot of projects have both CS source for development, with compiled JS for deployment. That might skew the stats between JS+CS, but it's a good indicator of CS' popularity compared to other languages.
Considering that, releases would be in JS, as they should be.
Once you are releasing things outside of your controlled/team environment using anything but JS is just a loop for others to jump through.