I've tried a lot of things but finally, including uninstall with the automated tools. So, I've uninstalled manually scikit-learn.
sudo rm -R /home/ubuntu/.local/lib/python3.6/site-packages/sklearn
sudo rm -R /home/ubuntu/.local/lib/python3.6/site-packages/scikit_learn-0.20.0-py3.6.egg-info
And re-install using pip
sudo pip3.6 install -U scikit-learn
Hope that can help someone else!