Final dist filename change for JRuby 9000.

Sorry for the additional change...but as far as I can tell, JRuby 9000 is the only build in here using a snapshot/nightly, and things have been in flux. Once we have releases of 9000 we can update this again and it should be ok.

I would like to clarify, however, how snapshot/nightly builds are supposed to work in ruby-build. As we rev JRuby, the snapshot builds will change.... 9.0.0.1-SNAPSHOT and so on. Should we make the filename the same for snapshots on a given branch or something?