script/release.sh: fix off by 1 error in announce.${tagname}.mail.txt creation

script/release.sh: fix off by 1 error in announce.${tagname}.mail.txt creation

Pair-Programmed-With: Karolin Seeger <kseeger@samba.org>

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Karolin Seeger <kseeger@samba.org>
Autobuild-User(master): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(master): Thu Jan 12 15:34:25 CET 2017 on sn-devel-144

(cherry picked from commit 7870c645b79da647bae45b4dc95e7d6e9abcd91a)

Autobuild-User(v4-4-test): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(v4-4-test): Fri Jan 27 11:52:07 CET 2017 on sn-devel-144