AttributeError: 'dict_keys' object has no attribute 'sort'

when i call the method without params, it's raise the error:
AttributeError: 'dict_keys' object has no attribute 'sort'

```
from jos.client import JDClient

client = JDClient(key='key', secret='secret')
method = 'jingdong.areas.overseasProvince.get'
params = {
}
res = client.call(method, False)
print(res)
```