Add min sklearn version build

[trevorstephens]

somewhere in the build specify min supported python 3.8 to build on min supported skelarn v 1.0.2

for now that's the latest release so hard to check it's working

something like this should work:

if [[ ${{ matrix.python_version }} == '3.8'; then
python -m pip install sklearn==1.0.2;
python -m pip install joblib==1.0.0;
fi

python --version
python -c "import numpy; print('numpy %s' % numpy.__version__)"
python -c "import scipy; print('scipy %s' % scipy.__version__)"
python -c "import joblib; print('joblib %s' % joblib.__version__)"
python -c "import sklearn; print('sklearn %s' % sklearn.__version__)"