Slightly different way of going about the same thing as comment #2:
sudo -H python3.5 -m pip install -U six
I needed to call python3.5 explicitly since I have a newer version of python (3.6) installed, however update-notifier seems to be using the system-level install of python3.5.
Slightly different way of going about the same thing as comment #2:
sudo -H python3.5 -m pip install -U six
I needed to call python3.5 explicitly since I have a newer version of python (3.6) installed, however update-notifier seems to be using the system-level install of python3.5.