姬海涵

I think `ThresholdDetector` should add a switch. For blackframe, use `if frame_avg < self.threshold:`. For whiteframe, use `if frame_avg > self.threshold:`.

I tried on my MAC. It's no problem, right? ``` 2.6.3 :004 > Role.first BOLT UNSECURE: 6ms bolt://neo4j:...@localhost:7687 BOLT UNSECURE: 102ms bolt://neo4j:...@localhost:7687 BOLT UNSECURE: 2ms bolt://neo4j:...@localhost:7687 BOLT UNSECURE: 1ms bolt://neo4j:...@localhost:7687...