Update certifi to 2020.6.20

[pyup-bot]

This PR updates certifi from 2019.6.16 to 2020.6.20.

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

Links

• PyPI: https://pypi.org/project/certifi
• Docs: https://certifiio.readthedocs.io/en/latest/

[codecov-commenter]

Codecov Report

Merging #319 into master will increase coverage by 6.36%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           master      #319      +/-   ##
===========================================
+ Coverage   93.63%   100.00%   +6.36%     
===========================================
  Files          11        12       +1     
  Lines         110       116       +6     
===========================================
+ Hits          103       116      +13     
+ Misses          7         0       -7     

Impacted Files	Coverage Δ
libpythonpro/github_api.py	100.00% <ø> (+100.00%)	⬆️
...ythonpro/tests/test_spam/test_enviador_de_email.py	100.00% <100.00%> (ø)
...ests/test_spam/test_envio_para_base_de_usuarios.py	100.00% <100.00%> (ø)
libpythonpro/tests/test_spam/test_github_api.py	100.00% <100.00%> (ø)

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[pyup-bot]

Closing this in favor of #392