contrib: migrate off of a couple of bitbucket URLs
I noticed this when diffing the thg installer against Mercurial to see what was
missing. There are a handful of other URLs in i18n and extension example help
text if anyone cares to update those.
Differential Revision: https://phab.mercurial-scm.org/D12606
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}