Update link to docs (Jekyll 3 update)

homeassistant/components/sensor/arest.py

@@ -4,7 +4,7 @@ homeassistant.components.sensor.arest
 The arest sensor will consume an exposed aREST API of a device.
 
 For more details about this platform, please refer to the documentation at
-https://home-assistant.io/components/sensor.arest.html
+https://home-assistant.io/components/sensor.arest/
 """
 import logging
 import requests