handles the DOI attribute

[azneto]

This pull request addresses issue #...

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[codecov-commenter]

Codecov Report

Merging #309 (8227ff3) into master (2e4dee2) will decrease coverage by 0.12%.
The diff coverage is 12.50%.

@@            Coverage Diff             @@
##           master     #309      +/-   ##
==========================================
- Coverage   69.35%   69.23%   -0.13%     
==========================================
  Files          30       30              
  Lines        4020     4027       +7     
  Branches      226      227       +1     
==========================================
  Hits         2788     2788              
- Misses       1175     1181       +6     
- Partials       57       58       +1     

Impacted Files	Coverage Δ
machado/loaders/featureattributes.py	77.89% <12.50%> (-6.20%)	⬇️

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