Fix spelling in lcb_behavior_get_syncmode man page

Change-Id: I46e2d3b87757818573621a5f767c1b65b7816f99
Reviewed-on: http://review.couchbase.org/25017
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Volker Mische <volker.mische@gmail.com>