minirst: respect escaping in definition list key
If we start adding `:` in command names… we need minirst to not choke on them.
Differential Revision: https://phab.mercurial-scm.org/D9869
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}