Fix SWF continue_as_new_workflow_execution start_to_close_timeout.

This fixes a typo. As per [SWF docs](http://docs.aws.amazon.com/amazonswf/latest/apireference/API_ContinueAsNewWorkflowExecutionDecisionAttributes.html) the correct name for `start_to_close_timeout` argument in `continue_as_new_workflow_execution` method should be `taskStartToCloseTimeout`.

I couldn't find any unittests for `layer1_decisions` module so I've added a new file with only this specific test case. It can be expanded later if other bugs are found or if someone has the time to contribute the missing ones.