Update scikit-learn to 0.21.0

[pyup-bot]

This PR updates scikit-learn from 0.20.0 to 0.21.0.

Changelog

0.20.3

A bug-fix release in the 0.20 series, supporting Python 2 and 3

0.20.2

Bug-fix release to the 0.20 branch, supporting Python 2 and 3

0.20.1

Released 21 November 2018.

See changelog at https://scikit-learn.org/0.20/whats_new.htmlversion-0-20-1

Links

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

[pyup-bot]

Closing this in favor of #106