setup.py calls for "sklearn," which is a deprecated alias for "scikit-learn"

[combs]

https://github.com/unitn-sml/pyconstruct/blob/f7174b00f16e34ca582bb1923ef46e871fc892b9/setup.py#L59

Here's a description of the problem-- https://pypi.org/project/sklearn/

In essence, it seems like sklearn should be replaced by scikit-learn

Thanks, Chris