"Unable to auto-detect BLED112 serial port" when connecting to Muse via example_plot.py

[bncuthbert]

On branch develop, commit b75051858452a1887d4d146d9c75657fab9a40c5. MacOS High Sierra 10.13.6. Python 3.6.5.

benc$ python example_plot.py
WARNING: No module named 'pexpect'
Traceback (most recent call last):
  File "/Users/benc/dev/merlin/py3.6/lib/python3.6/site-packages/pygatt/backends/bgapi/bgapi.py", line 155, in _open_serial_port
    serial_port = self._serial_port or self._detect_device_port()
  File "/Users/benc/dev/merlin/py3.6/lib/python3.6/site-packages/pygatt/backends/bgapi/bgapi.py", line 131, in _detect_device_port
    raise BGAPIError("Unable to auto-detect BLED112 serial port")
pygatt.backends.bgapi.exceptions.BGAPIError: Unable to auto-detect BLED112 serial port