Unless the cloning method you're using is really weird and badly corrupts something, it should react exactly like a regular Pokémon, and stay shiny after evolution. I'm not aware of any cloning methods that would affect shininess like this, but then again, I don't really know any Gen VII cloning methods at all, so I guess it's a possibility (although I doubt it). If you want to be safe, you could save your game before evolving the Pokémon and reset if anything bad happens.
