.arcconfig

hghave: deal with "rc" release

Without this change, 5.0rc0 is not recognised as 5.0

{
    "conduit_uri": "https://phab.mercurial-scm.org/api",
    "repository.callsign": "HG",
    "arc.land.onto.default": "@",
    "base": "hg:.^"
}