(#172) Added nuget package caching
(#172) Added nuget package caching

- Now that the Pull Request issues in AppVeyor have been correct, we can add back in the nuget package caching, which should speed up the build somewhat.

paladique/ChocolateyGUI,gep13/ChocolateyGUI,chocolatey/ChocolateyGUI,M-Zuber/ChocolateyGUI,chocolatey/ChocolateyGUI,sayedihashimi/ChocolateyGUI,gep13/ChocolateyGUI,wjk/ChocolateyGUI,RichiCoder1/ChocolateyGUI,digital-carver/ChocolateyGUI,chocolatey/ChocolateyGUI,gep13/ChocolateyGUI,gep13/ChocolateyGUI,alephnaughty/ChocolateyGUI,paladique/ChocolateyGUI,gep13/ChocolateyGUI,chocolatey/ChocolateyGUI,chocolatey/ChocolateyGUI,dlsteuer/ChocolateyGUI