git.1: switch homepage for stats

According to http://meta.ohloh.net/2014/07/black-duck-open-hub/
the site name of ohloh changed to openhub.

Change the man page accordingly.

Signed-off-by: Stefan Beller <stefanbeller@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git.txt

@@ -1044,7 +1044,7 @@ Authors
 -------
 Git was started by Linus Torvalds, and is currently maintained by Junio
 C Hamano. Numerous contributions have come from the Git mailing list
-<git@vger.kernel.org>.  http://www.ohloh.net/p/git/contributors/summary
+<git@vger.kernel.org>.  http://www.openhub.net/p/git/contributors/summary
 gives you a more complete list of contributors.
 
 If you have a clone of git.git itself, the