Update docker file to use the latest python image

[Meallia]

cf #304 Use the 3-slim rolling tag instead of using a fixed python version.

[codecov[bot]]

Codecov Report

Merging #359 (5175184) into master (7d1448e) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #359   +/-   ##
=======================================
  Coverage   69.51%   69.51%           
=======================================
  Files           8        8           
  Lines         538      538           
=======================================
  Hits          374      374           
  Misses        164      164           

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