chore: added support for Python 3.9

[bednar]

Proposed Changes

Added support for Python 3.9.

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• pytest tests completes successfully
• Commit messages are in semantic format
• Sign CLA (if not already signed)

[codecov-io]

Codecov Report

Merging #163 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #163   +/-   ##
=======================================
  Coverage   89.06%   89.06%           
=======================================
  Files          26       26           
  Lines        1939     1939           
=======================================
  Hits         1727     1727           
  Misses        212      212           

Impacted Files	Coverage Δ
setup.py	0.00% <ø> (ø)

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