Use keyword args for echo & trigger in DistanceSensor example

Author: bennuttall

gpiozero/input_devices.py

@@ -534,7 +534,7 @@ class DistanceSensor(SmoothedInputDevice):
         from gpiozero import DistanceSensor
         from time import sleep
 
-        sensor = DistanceSensor(18, 17)
+        sensor = DistanceSensor(echo=18, trigger=17)
         while True:
             print('Distance: ', sensor.distance * 100)
             sleep(1)