Fix docs typo (setMulti returns CAS values not boolean).

Change-Id: Id408fb8c3790094a02aa47fde84ced4189fb3827
Reviewed-on: http://review.couchbase.org/36558
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Brett Lawson <brett19@gmail.com>