asciidoc > 8.6.0 is a build requirement

[Eric S. Raymond]

Jason Azze <jason at azze.org>:
> I started to try every released asciidoc version between 8.4.5 and
> 8.6.8 from https://github.com/asciidoc/asciidoc/releases until I found
> the version where the error disappeared. 8.6.0 is the winner.

Thanks, I've added that to the requirements in INSTALL.
-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>