.mailmap: Map "H.Merijn Brand" to "H. Merijn Brand"

.mailmap: Map "H.Merijn Brand" to "H. Merijn Brand"

This patch was created by searching for duplicates of email addresses
in the shortlog by
    git shortlog -sne |awk '{ print $NF }' |sort |uniq -d

This will yield all email addresses, which are found multiple times within
the shortlog. We can assume that commiters having the same email address
are indeed the same person.

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