Update protobuf to 3.8.0

[pyup-bot]

This PR updates protobuf from 3.6.1 to 3.8.0.

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

@@          Coverage Diff          @@
##           master   #778   +/-   ##
=====================================
  Coverage      94%    94%           
=====================================
  Files          10     10           
  Lines         784    784           
=====================================
  Hits          737    737           
  Misses         47     47

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[pyup-bot]

Closing this in favor of #806