.arcconfig

setup: use raw string for regular expression

Otherwise Python 3.8 complains about the backslash.

Differential Revision: https://phab.mercurial-scm.org/D6202

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