Specify the value as bytes for bench example

Change-Id: Iaecd99f096b9316c5f82392cf63ec1776eab1054
Reviewed-on: http://review.couchbase.org/26285
Reviewed-by: Mordechai Nunberg <mnunberg@haskalah.org>
Tested-by: Mordechai Nunberg <mnunberg@haskalah.org>