Minor spelling correction in samba-tool domain

Signed-Off-By: Daniel Cotton <danielcotton.patches at gmail.com>
Reviewed-By: Michael Adam <obnox@samba.org>
Reviewed-By: Jelmer Vernooij <jelmer@samba.org>

Autobuild-User(master): Jelmer Vernooij <jelmer@samba.org>
Autobuild-Date(master): Tue Dec  2 01:18:53 CET 2014 on sn-devel-104