.mailmap: record canonical email for Richard Hansen

When I changed employers my work address changed from rhansen@bbn.com
to hansenr@google.com.  Rather than map my old work address to my new,
map them both to my permanent personal email address.  (I will still
use my work address in commits I submit so that my employer gets some
credit.)

Signed-off-by: Richard Hansen <hansenr@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.mailmap

@@ -192,6 +192,8 @@ Philippe Bruhat <book@cpan.org>
 Ralf Thielow <ralf.thielow@gmail.com> <ralf.thielow@googlemail.com>
 Ramsay Jones <ramsay@ramsayjones.plus.com> <ramsay@ramsay1.demon.co.uk>
 René Scharfe <l.s.r@web.de> <rene.scharfe@lsrfire.ath.cx>
+Richard Hansen <rhansen@rhansen.org> <hansenr@google.com>
+Richard Hansen <rhansen@rhansen.org> <rhansen@bbn.com>
 Robert Fitzsimons <robfitz@273k.net>
 Robert Shearman <robertshearman@gmail.com> <rob@codeweavers.com>
 Robert Zeh <robert.a.zeh@gmail.com>