CBQE-0: fix typo in task.py

Change-Id: I26f51c3ba6c73dbe76fce61ecb06bb6fad7e9c4a
Reviewed-on: http://review.couchbase.org/33609
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>