In my case, update the pip versión after create the venv, this update pip from 9.0.1 to 20.3.1
python3 -m venv env/python
source env/python/bin/activate
pip3 install pip --upgrade
But, the message was...
Using legacy 'setup.py install' for django-avatar, since package 'wheel' is not installed.
Then, I install wheel package after update pip
python3 -m venv env/python
source env/python/bin/activate
pip3 install --upgrade pip
pip3 install wheel
And the message was...
Building wheel for django-avatar (setup.py): started
default: Building wheel for django-avatar (setup.py): finished with status 'done'