windows: use abspath in convert.git
We replace `os.path.abspath` with `util.abspath`. This should solve more "drive
capitalization" issue on Windows.
Differential Revision: https://phab.mercurial-scm.org/D11070
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}