Updating the ruby-build package

[Adam Baxter <voltagex@voltagex.org>]

I raised a bug for updating the ruby-build package to the latest upstream version

I've made a mess of https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=807077 - the last message was me trying to send from Mutt to avoid further text formatting issues, but I've managed to encrypt rather than sign... sorry!

There are three issues at play:

* It'd be nice to get a newer version into Debian

* debian-stable may need a version bump to fix #701918 (or it might be able to be closed?)

* the Debian source for ruby-build (https://anonscm.debian.org/gitweb/?p=pkg-ruby-extras/ruby-build.git) doesn't build since the manpage was modified to use asciidoctor

Sorry for the noise on the bug tracker.

--Adam