Reset index of cutoff times in calculate feature matrix

[WillKoehrsen]

Addresses issue where duplicated indices in cutoff_time dataframe results in duplicated rows in the feature matrix with calculate_feature_matrix. Solution is to reset the index in cutoff_time to remove the duplicates.

[codecov-io]

Codecov Report

Merging #198 into master will increase coverage by 0.08%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #198      +/-   ##
=========================================
+ Coverage   93.21%   93.3%   +0.08%     
=========================================
  Files          70      70              
  Lines        7727    7734       +7     
=========================================
+ Hits         7203    7216      +13     
+ Misses        524     518       -6

Impacted Files	Coverage Δ
...computational_backends/calculate_feature_matrix.py	96.98% <100%> (ø)	⬆️
...utational_backend/test_calculate_feature_matrix.py	99.26% <100%> (ø)	⬆️
featuretools/primitives/binary_transform.py	90.75% <0%> (+3.46%)	⬆️

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[kmax12]

Looks good. Merging!