fix colorwheel location

Apparently _pixelbuf no longer has colorwheel in it (adafruit/circuitpython#4992). But it does live in the builtin rainbowio lib,

Author: dborne

Adafruit_MacroPad/MacroPad/code.py

@@ -4,7 +4,7 @@
 import rotaryio
 import neopixel
 import keypad
-from _pixelbuf import colorwheel
+from rainbowio import colorwheel
 
 
 key_pins = (board.KEY1, board.KEY2, board.KEY3, board.KEY4, board.KEY5, board.KEY6,