Update .mailmap

Author: hkmatsumoto

Diff for: .mailmap

@@ -113,6 +113,7 @@ Hanna Kruppe <hanna.kruppe@gmail.com> <robin.kruppe@gmail.com>
 Heather <heather@cynede.net> <Cynede@Gentoo.org>
 Heather <heather@cynede.net> <Heather@cynede.net>
 Herman J. Radtke III <herman@hermanradtke.com> Herman J. Radtke III <hermanradtke@gmail.com>
+Hirochika Matsumoto <git@hkmatsumoto.com> <matsujika@gmail.com>
 Ian Jackson <ijackson@chiark.greenend.org.uk> <ian.jackson@citrix.com>
 Ian Jackson <ijackson@chiark.greenend.org.uk> <ijackson+github@slimy.greenend.org.uk>
 Ian Jackson <ijackson@chiark.greenend.org.uk> <iwj@xenproject.org>