fix crash AttributeError: Worker instance has no attribute 'error_sleep'

```
File "/usr/lib/python2.7/site-packages/dwhois-0.11-py2.7.egg/EGG-INFO/scripts/dwhois-worker", line 34, in <module>
File "build/bdist.linux-x86_64/egg/dwhois/worker.py", line 98, in queue
AttributeError: Worker instance has no attribute 'error_sleep'
```