Use COPY instead of ADD in Dockerfile

[gy741]

Hello,

The use of COPY is preferred over ADD when additional functionalities of ADD are not being used (like spraying the contents of a tar in a folder).

Ref: https://docs.docker.com/engine/articles/dockerfile_best-practices/#add-or-copy

Thanks.

[codecov]

Codecov Report

Merging #502 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #502   +/-   ##
======================================
  Coverage    65.8%   65.8%           
======================================
  Files          11      11           
  Lines        1000    1000           
======================================
  Hits          658     658           
  Misses        305     305           
  Partials       37      37

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[robertojrojas]

LGTM