make sure data set is downloaded for appveyor.yml

[jGaboardi]

This PR adds a command in appveyor to download the proper examples datasets.

[codecov]

Codecov Report

Merging #419 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #419      +/-   ##
==========================================
+ Coverage   98.07%   98.07%   +<.01%     
==========================================
  Files           5        5              
  Lines        1768     1770       +2     
  Branches      220      220              
==========================================
+ Hits         1734     1736       +2     
  Misses         14       14              
  Partials       20       20

Impacted Files	Coverage Δ
spaghetti/tests/test_network_api.py	100% <100%> (ø)	⬆️
spaghetti/tests/test_network.py	100% <100%> (ø)	⬆️

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