Update codecov to 2.0.21

[pyup-bot]

This PR updates codecov from 2.0.16 to 2.0.21.

Changelog

2.0.21

- fixed string issues

2.0.20

- fixed broken subprocess handling

2.0.19

- fixed broken subprocess handling

2.0.18

- fixed broken subprocess handling

2.0.17

- fixed reported command injection vulnerability.

Links

• PyPI: https://pypi.org/project/codecov
• Changelog: https://pyup.io/changelogs/codecov/
• Repo: https://github.com/codecov/codecov-python

[codecov]

Codecov Report

Merging #222 into master will not change coverage by %.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #222   +/-   ##
=======================================
  Coverage   69.91%   69.91%           
=======================================
  Files          16       16           
  Lines        1569     1569           
=======================================
  Hits         1097     1097           
  Misses        472      472           

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[pyup-bot]

Closing this in favor of #223