Permit - in URL schemes for special URLs

Clients might be using their own special git-remote-* helper that
has a hypen in its name. Permit - in the scheme part of the URL
when trying to decide if it is an SSH URL and assume it is *not*
SSH if the URL matches "foo-bar://" style.

Change-Id: I7ba2d810a614f6e605a441d5972902c4a14e73fd