loader: Change VK_LAYERS_FOLDERS to VK_LAYER_FOLDERS to match documentation
loader: Change VK_LAYERS_FOLDERS to VK_LAYER_FOLDERS to match documentation

This effects Windows layers.

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