Update scikit_learn to 0.23.1

[pyup-bot]

This PR updates scikit_learn from 0.22 to 0.23.1.

Changelog

0.23.0

We're happy to announce the 0.23 release. You can read
the release highlights under https://scikit-learn.org/stable/auto_examples/release_highlights/plot_release_highlights_0_23_0.html
and the long version of the change log under https://scikit-learn.org/stable/whats_new/v0.23.htmlversion-0-23-0

This version supports Python versions 3.6 to 3.8.

0.22.2.post1

We're happy to announce the 0.22.2.post1 bugfix release. 

The 0.22.2.post1 release includes a packaging fix for the source distribution
but the content of the packages is otherwise identical to the content of the
wheels with the 0.22.2 version (without the .post1 suffix).

Change log under https://scikit-learn.org/stable/whats_new/v0.22.htmlchanges-0-22-2.

This version supports Python versions 3.5 to 3.8.

0.22.1

We're happy to announce the 0.22.1 bugfix release. 
Change log under https://scikit-learn.org/stable/whats_new/v0.22.htmlchanges-0-22-1.

This version supports Python versions 3.5 to 3.8.

Links

• PyPI: https://pypi.org/project/scikit-learn
• Changelog: https://pyup.io/changelogs/scikit-learn/
• Homepage: http://scikit-learn.org