Update attrs to 20.3.0#277

pyup-bot wants to merge 2 commits intomasterjoaogarciadelima/libpythonpro:masterfrom

pyup-update-attrs-19.3.0-to-20.3.0joaogarciadelima/libpythonpro:pyup-update-attrs-19.3.0-to-20.3.0Copy head branch name to clipboard