Handle parquet serialization with last time index

[kmax12]

Handles cases where we are serializing an entityset with a last time index. Also added test

Fixes #202

[codecov-io]

Codecov Report

Merging #204 into master will increase coverage by 0.05%.
The diff coverage is 90%.

@@            Coverage Diff             @@
##           master     #204      +/-   ##
==========================================
+ Coverage    93.3%   93.35%   +0.05%     
==========================================
  Files          70       70              
  Lines        7734     7737       +3     
==========================================
+ Hits         7216     7223       +7     
+ Misses        518      514       -4

Impacted Files	Coverage Δ
featuretools/entityset/serialization.py	91.66% <ø> (+3.57%)	⬆️
featuretools/tests/entityset_tests/test_es.py	99.31% <90%> (-0.22%)	⬇️

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[rwedge]

Looks good