MacOS build issue #7
Description
For those that run on MacOS, you'll not only need the change called out in #4 to get you past the command error, you'll also need to change the command from python to python3 for the macOS command (tools.uf2conv.cmd.macosx) as well as add the execution bit to tools/adafruit-nrfutil/macos/adafruit-nrfutil (e.g. chmod 755 tools/adafruit-nrfutil/macos/adafruit-nrfuti) to get things to building.