build: Change appveyor to build VS 2013 and 2015
build: Change appveyor to build VS 2013 and 2015

Change-Id: Idccb248aa46a5028b9c28d5487760c749a8d61e2

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools