Update coverage to 4.5.4

[pyup-bot]

This PR updates coverage from 4.5.3 to 4.5.4.

Changelog

4.5.4

---------------------------

- Multiprocessing support in Python 3.8 was broken, but is now fixed.  Closes
`issue 828`_.

.. _issue 828: https://github.com/nedbat/coveragepy/issues/828


.. _changes_453:

Links

• PyPI: https://pypi.org/project/coverage
• Changelog: https://pyup.io/changelogs/coverage/
• Repo: https://github.com/nedbat/coveragepy

[coveralls]

Pull Request Test Coverage Report for Build 403

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.75%

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Totals
Change from base Build 398:	0.0%
Covered Lines:	45
Relevant Lines:	48

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💛 - Coveralls