mtools: update upstream URL
The previously specified tux.org URL did not appear to be maintained.
The gnu.org URL looks better maintained and is the same domain as the
actual tarball download.
Signed-off-by: Frank Hunleth <fhunleth@troodon-software.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Frank Hunleth