Added AppVeyor build cache for NuGet packages.
Added AppVeyor build cache for NuGet packages.

andycmaj/cake,patriksvensson/cake,ferventcoder/cake,UnbelievablyRitchie/cake,patriksvensson/cake,Sam13/cake,phenixdotnet/cake,robgha01/cake,phrusher/cake,michael-wolfenden/cake,mholo65/cake,danielrozo/cake,gep13/cake,robgha01/cake,daveaglick/cake,UnbelievablyRitchie/cake,wallymathieu/cake,DixonD-git/cake,cake-build/cake,thomaslevesque/cake,Sam13/cake,Julien-Mialon/cake,Invenietis/cake,cake-build/cake,adamhathcock/cake,yvschmid/cake,RichiCoder1/cake,RehanSaeed/cake,gep13/cake,SharpeRAD/Cake,danielrozo/cake,devlead/cake,thomaslevesque/cake,ferventcoder/cake,andycmaj/cake,yvschmid/cake,jrnail23/cake,daveaglick/cake,phenixdotnet/cake,Invenietis/cake,Julien-Mialon/cake,vlesierse/cake,vlesierse/cake,os-alan/cake,marcosnz/cake,michael-wolfenden/cake,phrusher/cake,SharpeRAD/Cake,devlead/cake,adamhathcock/cake,DavidDeSloovere/cake,marcosnz/cake,RichiCoder1/cake,jrnail23/cake,mholo65/cake,RehanSaeed/cake