Change display use to bytes

[caternuson]

For #56. Simple change from list to bytes. Recreated original issue and confirmed this fix works.

This is saved as tft_test.py

import time
import board
import busio
import displayio
from adafruit_featherwing import minitft_featherwing

i2c = board.I2C()
spi = busio.SPI(board.SCK1, board.MOSI1, board.MISO1)
fw = minitft_featherwing.MiniTFTFeatherWing(i2c=i2c, spi=spi, cs=board.GP15, dc=board.GP14)

bmp = displayio.Bitmap(160, 80, 2)

pal = displayio.Palette(2)
pal[0] = 0x000000
pal[1] = 0xffffff

tg = displayio.TileGrid(bmp, pixel_shader=pal)

splash = displayio.Group()
splash.append(tg)

fw.display.show(splash)

for x in range(40, 100):
    for y in range(30, 50):
        bmp[x, y] = 1

fw.display.refresh()

Running that with:

$ export BLINKA_U2IF=1
$ python3 tft_test.py

gets: