Fix tox requirements conflicts for 20.12LTS

[ashleysommer]

Like #2027 but for 20.12LTS

[codecov]

Codecov Report

Merging #2029 (760c74a) into 20.12LTS (04be8e9) will increase coverage by 0.09%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           20.12LTS    #2029      +/-   ##
============================================
+ Coverage     92.70%   92.79%   +0.09%     
============================================
  Files            29       29              
  Lines          3262     3262              
  Branches        571      571              
============================================
+ Hits           3024     3027       +3     
+ Misses          161      159       -2     
+ Partials         77       76       -1     

Impacted Files	Coverage Δ
sanic/server.py	81.61% <0.00%> (+0.56%)	⬆️

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