Change manpage repository address to github.

doc/gitstats.pod

 
 B<gitstats> was written by Heikki Hokkanen and others.
 
-See the git repository at http://repo.or.cz/w/gitstats.git for an up-to-date full list of contributors.
+See the git repository at https://github.com/hoxu/gitstats for an up-to-date full list of contributors.
 
 =head1 WWW