Docker images with missing prophet fix

[martins0n]

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• Did you read the contribution guide?
• Did you update the docs? We use Numpy format for all the methods and classes.
• Did you write any new necessary tests?
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• Examples / docs / tutorials / contributors update
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[github-actions]

🚀 Deployed on https://deploy-preview-767--etna-docs.netlify.app

[codecov-commenter]

Codecov Report

Merging #767 (b99bef0) into master (e40ed7a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #767   +/-   ##
=======================================
  Coverage   83.57%   83.57%           
=======================================
  Files         122      122           
  Lines        6776     6776           
=======================================
  Hits         5663     5663           
  Misses       1113     1113           

📣 Codecov can now indicate which changes are the most critical in Pull Requests. Learn more

[iKintosh]

Still strange why pip does not install prophet from requirement.txt file. But if that allows to fix the bug then LGTM