RFS: new version of asciidoctor (1.5.8-1) ready for review/upload

[Joseph Herlant <aerostitch@debian.org>]

Hi guys,

I've updated the asciidoctor package with the latest 1.5.8 version of
asciidoctor.
It fixes 2 bugs: #913892 which is a CVE and #909105 which currently
blocks some packages like ndctl from being available on ia64 (see the
last comments at the end of #909105).

It is available in https://salsa.debian.org/ruby-team/asciidoctor

Could you have a look when you have a moment to review the changes please?
I can't currently upload the package myself as I'm waiting for the
debian-keyring to be uploaded.

Thanks for your help,
Joseph