`default.nix` no longer works due to PyUSB incompatibilty

[aeblyve]

running nix-build or nix-shell default.nix fails, with:

Finished executing setuptoolsBuildPhase
installing
Executing pipInstallPhase
/build/pyusb-1.2.1/dist /build/pyusb-1.2.1
DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. More details about Python 2 support in pip can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support pip 21.0 will remove support for this functionality.
Processing ./pyusb-1.2.1-py2-none-any.whl
ERROR: Package 'pyusb' requires a different Python: 2.7.18 not in '>=3.6.0'
error: builder for '/nix/store/5sb1f0d71w8337mslr468cxjahkq3q93-python2.7-pyusb-1.2.1.drv' failed with exit code 1;
       last 10 log lines:
       > adding 'pyusb-1.2.1.dist-info/top_level.txt'
       > adding 'pyusb-1.2.1.dist-info/RECORD'
       > removing build/bdist.linux-x86_64/wheel
       > Finished executing setuptoolsBuildPhase
       > installing
       > Executing pipInstallPhase
       > /build/pyusb-1.2.1/dist /build/pyusb-1.2.1
       > DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. More details about Python 2 support in pip can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support pip 21.0 will remove support for this functionality.
       > Processing ./pyusb-1.2.1-py2-none-any.whl
       > ERROR: Package 'pyusb' requires a different Python: 2.7.18 not in '>=3.6.0'
       For full logs, run 'nix log /nix/store/5sb1f0d71w8337mslr468cxjahkq3q93-python2.7-pyusb-1.2.1.drv'.

To reproduce, simply run nix-build or nix-shell default.nix. Expected behavior: I enter a shell where I can build/flash the firmware.