Difficulty upgrading past 0.1.4 on Debian Jessie

Debian Jessie comes with asciidoctor 0.1.4 in its repositories.

Trying to update with e.g 'sudo gem update asciidoctor' just generates

> Updating installed gems
> Nothing to update

(Speaking as a complete ruby newbie) how can I get the current
asciidoctor installed?

Thanks,

Jon

OK, I see that the Debian default install of asciidoctor seems to be under
/usr/lib/ruby/vendor_ruby/, while 'gem update' puts the newer 1.5.4 version
under /var/lib/gems/2.1.0/gems/ with the invocation script in
/usr/local/bin/asciidoctor instead of /usr/bin. So it was getting installed,
but not visible on my search path. Added PR !1733 to try and document
this in README.adoc.

Jon