.mailmap: fix broken entry for Martin Langhoff

Commit adc3192 (Martin Langhoff has a new e-mail address,
2010-10-05) added a mailmap entry, but forgot that both the
old and new email addresses need to appear for one to be
mapped to the other (i.e., we do not key mailmap emails by
name).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.mailmap

@@ -54,7 +54,7 @@ Li Hong <leehong@pku.edu.cn>
 Lukas Sandström <lukass@etek.chalmers.se>
 Marc-André Lureau <marcandre.lureau@gmail.com>
 Mark Rada <marada@uwaterloo.ca>
-Martin Langhoff <martin@laptop.org>
+Martin Langhoff <martin@laptop.org> <martin@catalyst.net.nz>
 Martin von Zweigbergk <martinvonz@gmail.com> <martin.von.zweigbergk@gmail.com>
 Michael Coleman <tutufan@gmail.com>
 Michael J Gruber <git@drmicha.warpmail.net> <michaeljgruber+gmane@fastmail.fm>