fix netdico version (requirements_all.txt mismatch)
> # homeassistant.components.discovery
> netdisco==2.2.0
in https://github.com/home-assistant/home-assistant/blob/0.83.0/requirements_all.txt
however:
> 2019-03-03 14:47:19 INFO (SyncWorker_14) [homeassistant.util.package] Attempting install of netdisco==2.1.0