add python 3.9 support

[tsv1]

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[codecov-commenter]

Codecov Report

Merging #18 (fe365a8) into master (b6c0135) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #18   +/-   ##
=======================================
  Coverage   96.84%   96.85%           
=======================================
  Files          71       71           
  Lines        1460     1461    +1     
  Branches      110      110           
=======================================
+ Hits         1414     1415    +1     
  Misses         42       42           
  Partials        4        4           

Impacted Files	Coverage Δ
jj/_core.py	65.15% <ø> (ø)
jj/responses/_response.py	98.73% <100.00%> (+0.01%)	⬆️

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