Add Python 3.9 support

[ymyzk]

No description provided.

[codecov]

Codecov Report

Merging #65 (aef9d86) into master (d73039b) will increase coverage by 1.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #65      +/-   ##
==========================================
+ Coverage   52.18%   53.21%   +1.02%     
==========================================
  Files           8        8              
  Lines         320      327       +7     
  Branches       42       42              
==========================================
+ Hits          167      174       +7     
  Misses        151      151              
  Partials        2        2              

Impacted Files	Coverage Δ
wsgi_lineprof/writers.py	97.36% <0.00%> (ø)
wsgi_lineprof/formatter.py	33.33% <0.00%> (+0.93%)	⬆️
wsgi_lineprof/filters.py	54.76% <0.00%> (+1.10%)	⬆️
wsgi_lineprof/stats.py	72.22% <0.00%> (+4.48%)	⬆️

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