updated doc/ns-server-hierarchy.txt for upr_notifier

Change-Id: Ib958f84a2202ced81ba8654d0b92217d14ec6084
Reviewed-on: http://review.couchbase.org/35915
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>