Update execution description failed

[Lingxian Kong]

send rest api to update execution's description, an error will occur.

# http PUT http://127.0.0.1:8989/v2/executions/81dcd446-b7b3-4881-831a-d6bbdff79bc3 description=my_second
HTTP/1.0 500 Internal Server Error
Content-Length: 137
Content-Type: application/json; charset=UTF-8
Date: Sat, 20 Jun 2015 14:17:51 GMT
Server: WSGIServer/0.1 Python/2.7.3

{
    "debuginfo": null,
    "faultcode": "Server",
    "faultstring": "update_workflow_execution() got an unexpected keyword argument 'description'"
}