pip 18.1: pipenv graph results in ImportError: cannot import name 'get_installed_distributions'

I'm currently using

python3 -m pip install pip==10.0.1
python3 -m pip install pipenv==2018.5.18

Once #2924 is fixed and released, you can upgrade again to the latest and greatest.

python3 -m pip install --upgrade pip
python3 -m pip install --upgrade pipenv