Fix progress bar undercounting

[kmax12]

The current logic undercounts the progress. This PR fixes how we do the count.

Added a test case

[codecov]

Codecov Report

Merging #743 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #743      +/-   ##
==========================================
+ Coverage   97.65%   97.65%   +<.01%     
==========================================
  Files         118      118              
  Lines       10356    10364       +8     
==========================================
+ Hits        10113    10121       +8     
  Misses        243      243

Impacted Files	Coverage Δ
featuretools/tests/synthesis/test_dfs_method.py	100% <100%> (ø)	⬆️
...computational_backends/calculate_feature_matrix.py	98.23% <100%> (ø)	⬆️
...utational_backend/test_calculate_feature_matrix.py	99.37% <100%> (ø)	⬆️
...s/computational_backends/feature_set_calculator.py	98.23% <100%> (ø)	⬆️

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[angela97lin]

LGTM! Glad you were able to track down the num_features undercounting!