fix sklearn release circle ci [temporary]
new sklearn release (https://github.com/scikit-learn/scikit-learn/releases) seems to be broken or leads to errors for PR since this morning - go back to previous version for now to avoid circle ci errors
@julien-c this should fix the sklearn problem for the moment<|||||>👍 
<|||||>reverted on master as they pushed a fixed release right after that one.