use git remote command to fetch remote urls

If the git url.<base>.insteadOf or url.<base>.pushInsteadOf options are
used, the URL listed in the config directly may not be the real URL used
for fetching.  The remote command will resolve the real URLs git will be
using, so use that instead.
Merge pull request #6 from haarg/remote-not-config

use git remote command to fetch remote urls