Run CodeCov through github actions and remove Tox

[rogebrd]

Travis was setup not to build on pushes which meant that when a pull request was pushed to master, it would not update coverage. Because of this, I added a github action to do so. Since the travis config has been updated, we will use travis to publish code coverage.

[codecov]

Codecov Report

Merging #225 into master will decrease coverage by 4.83%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #225      +/-   ##
==========================================
- Coverage   51.81%   46.98%   -4.84%     
==========================================
  Files          32       32              
  Lines       85096    77334    -7762     
  Branches     6370     6370              
==========================================
- Hits        44096    36332    -7764     
- Misses      40949    40951       +2     
  Partials       51       51              

Flag	Coverage Δ
#unit	46.98% <ø> (?)
#unittests	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
dropbox/users.py	41.83% <0.00%> (-6.37%)	⬇️
dropbox/secondary_emails.py	42.59% <0.00%> (-5.75%)	⬇️
dropbox/team.py	46.13% <0.00%> (-5.23%)	⬇️
dropbox/sharing.py	46.11% <0.00%> (-5.08%)	⬇️
dropbox/files.py	47.04% <0.00%> (-5.02%)	⬇️
dropbox/cloud_docs.py	47.32% <0.00%> (-5.01%)	⬇️
dropbox/team_log.py	47.37% <0.00%> (-5.00%)	⬇️
dropbox/file_requests.py	47.07% <0.00%> (-5.00%)	⬇️
dropbox/file_properties.py	48.98% <0.00%> (-4.69%)	⬇️
dropbox/paper.py	49.73% <0.00%> (-4.46%)	⬇️
... and 14 more

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