added runtime dep for airvisual sensor platform

https://www.home-assistant.io/components/sensor.airvisual/

runtime-requirements.txt

@@ -7,6 +7,7 @@ flux_led==0.21
 gTTS-token==1.1.2
 mutagen==1.41.1
 netdisco==2.1.0
+pyairvisual==2.0.1
 pydispatcher==2.0.5
 pyotp==2.2.6
 sqlalchemy==1.2.11