.arcconfig

index: fix a comment about overflow-checking

There's no "argument-checking" done in this method. This was a bad
copy paste.

Differential Revision: https://phab.mercurial-scm.org/D4339

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