Replace deprecated datetime.utcfromtimestamp() with timezone-aware date

[VMRuiz]

Fix #182

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.02%. Comparing base (db0de6e) to head (bb8f7b7).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #183   +/-   ##
=======================================
  Coverage   94.02%   94.02%           
=======================================
  Files          28       28           
  Lines        1958     1958           
=======================================
  Hits         1841     1841           
  Misses        117      117           

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