Remove rtype from task clone() doc
Remove rtype from task clone() doc

The sphinx docs don't seem to show this parameter
correctly when building the html docs so instead of
showing it just remove since the return type should
be pretty obvious due to the surronding text.

Change-Id: Id27c23d79d7fdbcd677ed959d9d817c796a0828c

pombredanne/taskflow-1,openstack/taskflow,pombredanne/taskflow-1,jimbobhickville/taskflow,junneyang/taskflow,openstack/taskflow,junneyang/taskflow,jimbobhickville/taskflow