Install black_nbconvert in testenv

Author: aseyboldt

scripts/create_testenv.sh

@@ -37,6 +37,7 @@ conda update --yes --all
 conda install --yes python-graphviz ipywidgets
 conda install --yes --file requirements.txt
 conda install --yes --file requirements-dev.txt
+pip install --no-cache-dir --force-reinstall black_nbconvert
 
 #  Install editable using the setup.py
 if [ -z ${NO_SETUP} ]; then