Remove PostgreSQL exposed port from docker-compose.yml

[akondas]

Closes #409

[codecov]

Codecov Report

Merging #410 (ba5a69b) into master (3540583) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #410   +/-   ##
=========================================
  Coverage     99.38%   99.38%           
  Complexity     1862     1862           
=========================================
  Files           297      297           
  Lines          5867     5867           
=========================================
  Hits           5831     5831           
  Misses           36       36           

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