Update protobuf to 3.9.2

[pyup-bot]

This PR updates protobuf from 3.6.1 to 3.9.2.

The bot wasn't able to find a changelog for this release. Got an idea?

Links

• PyPI: https://pypi.org/project/protobuf
• Changelog: https://pyup.io/changelogs/protobuf/
• Repo: https://github.com/protocolbuffers/protobuf/releases
• Homepage: https://developers.google.com/protocol-buffers/

[codecov-io]

Codecov Report

Merging #846 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #846   +/-   ##
=======================================
  Coverage   94.02%   94.02%           
=======================================
  Files          10       10           
  Lines         787      787           
=======================================
  Hits          740      740           
  Misses         47       47

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[pyup-bot]

Closing this in favor of #855