message: update edgetpu model
diff: board_size = 19
  players = {
  - "minigo_py" : Player("python"
  + "minigo_edgetpu" : Player("python"
  " -u"
  " gtp.py"
  - " --load_file=models/minigo_20190107_edgetpu.tflite"
  + " --load_file=saved_models/v17-2019-04-29-edgetpu.tflite"
  " --minigui_mode=true"
  " --num_readouts=800"
  " --resign_threshold=-0.8"
  