message: Add Python 3.9 classifier to the package configuration.
diff: @@ -284,6 +284,7 @@ def main():
  classifiers=[
  'Programming Language :: Python :: 3.7',
  'Programming Language :: Python :: 3.8',
  + 'Programming Language :: Python :: 3.9',
  'Topic :: Software Development :: Libraries',
  ],
  license='Apache 2.0',
  