Update .mailmap with "Michael"

Signed-off-by: Junio C Hamano <junkio@cox.net>

.mailmap

@@ -23,6 +23,7 @@ Lars Doelle <lars.doelle@on-line.de>
 Lars Doelle <lars.doelle@on-line ! de>
 Lukas Sandström <lukass@etek.chalmers.se>
 Martin Langhoff <martin@catalyst.net.nz>
+Michele Ballabio <barra_cuda@katamail.com>
 Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
 Ramsay Allan Jones <ramsay@ramsay1.demon.co.uk>
 René Scharfe <rene.scharfe@lsrfire.ath.cx>