[Backend] Move to Python 3.8

[gchhablani]

IMPORTANT NOTES (please read, then delete):

• The PR title should start with "Fix #bugnum: " (if applicable), followed by a clear one-line present-tense summary of the changes introduced in the PR. For example: "Fix #bugnum: Introduce the first version of the collection editor.".

• Please make sure to mention "#bugnum" somewhere in the description of the PR. This enables GitHub to link the PR to the corresponding bug.

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[codecov-commenter]

Codecov Report

Merging #4239 (7b1a325) into master (96968d6) will decrease coverage by 3.63%.
Report is 1091 commits behind head on master.
The diff coverage is 46.30%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4239      +/-   ##
==========================================
- Coverage   72.93%   69.30%   -3.63%     
==========================================
  Files          83       20      -63     
  Lines        5368     3574    -1794     
==========================================
- Hits         3915     2477    -1438     
+ Misses       1453     1097     -356     

Files	Coverage Δ
frontend/src/js/controllers/ChallengeInviteCtrl.js	100.00% <100.00%> (ø)
frontend/src/js/controllers/SubmissionFilesCtrl.js	95.45% <100.00%> (ø)
frontend/src/js/controllers/analyticsCtrl.js	80.72% <ø> (ø)
frontend/src/js/controllers/changePwdCtrl.js	100.00% <100.00%> (ø)
frontend/src/js/controllers/contactUsCtrl.js	100.00% <100.00%> (ø)
frontend/src/js/controllers/dashCtrl.js	99.07% <100.00%> (+0.14%)	⬆️
...ontend/src/js/controllers/featuredChallengeCtrl.js	68.99% <100.00%> (ø)
frontend/src/js/controllers/hostedChallengeCtrl.js	100.00% <100.00%> (ø)
frontend/src/js/controllers/webCtrl.js	90.90% <100.00%> (ø)
...ntend/src/js/controllers/challengeHostTeamsCtrl.js	70.50% <66.66%> (-1.18%)	⬇️
... and 7 more

... and 63 files with indirect coverage changes

Files	Coverage Δ
frontend/src/js/controllers/ChallengeInviteCtrl.js	100.00% <100.00%> (ø)
frontend/src/js/controllers/SubmissionFilesCtrl.js	95.45% <100.00%> (ø)
frontend/src/js/controllers/analyticsCtrl.js	80.72% <ø> (ø)
frontend/src/js/controllers/changePwdCtrl.js	100.00% <100.00%> (ø)
frontend/src/js/controllers/contactUsCtrl.js	100.00% <100.00%> (ø)
frontend/src/js/controllers/dashCtrl.js	99.07% <100.00%> (+0.14%)	⬆️
...ontend/src/js/controllers/featuredChallengeCtrl.js	68.99% <100.00%> (ø)
frontend/src/js/controllers/hostedChallengeCtrl.js	100.00% <100.00%> (ø)
frontend/src/js/controllers/webCtrl.js	90.90% <100.00%> (ø)
...ntend/src/js/controllers/challengeHostTeamsCtrl.js	70.50% <66.66%> (-1.18%)	⬇️
... and 7 more

... and 63 files with indirect coverage changes

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