Update incorrect docs in tonePitchFollower example

The comments state that the speaker should be on pin 8, but the code references pin 9. Updated the comments to reflect the correct pin.

Author: mcoms

examples/02.Digital/tonePitchFollower/tonePitchFollower.ino

@@ -4,7 +4,7 @@
  Plays a pitch that changes based on a changing analog input
  
  circuit:
- * 8-ohm speaker on digital pin 8
+ * 8-ohm speaker on digital pin 9
  * photoresistor on analog 0 to 5V
  * 4.7K resistor on analog 0 to ground