#31 use venv for virtualenv operations

( . "build/venv/bin/activate" && "python3" -m pip install --upgrade -r "requirements.txt" )

build/venv/bin/python -m pip install --upgrade -r requirements.txt

replace ```shell ( . "build/venv/bin/activate" && "python3" -m pip install --upgrade -r "requirements.txt" ) ``` with ```shell build/venv/bin/python -m pip install --upgrade -r requirements.txt ```

Probably fixed in e498c5d06fecbc8afca6ff1a1e6ef592cd87ba3c.