PYCBC-155 [docs] Fix parameter name mismatch

Change-Id: Icc6a45a35c373ebb9ec16e6676bdb1fded94287b
Reviewed-on: http://review.couchbase.org/27622
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>