Bump base image to Ubuntu 20.04 (related to #244)

[vania-pooh]

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[codecov]

Codecov Report

Merging #344 (91848cb) into master (a8deaac) will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #344   +/-   ##
======================================
  Coverage    6.40%   6.40%           
======================================
  Files           7       7           
  Lines         765     765           
======================================
  Hits           49      49           
  Misses        709     709           
  Partials        7       7           

Flag	Coverage Δ
go	6.40% <ø> (ø)

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