Exclude test sources from codecov

[dmsurti]

Exclude Code/Model/Tests/* files from coverage.

[codecov-io]

Codecov Report

Merging #69 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master     #69   +/-   ##
======================================
  Coverage    69.3%   69.3%           
======================================
  Files          16      16           
  Lines        1492    1492           
  Branches      143     143           
======================================
  Hits         1034    1034           
  Misses        390     390           
  Partials       68      68

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