flatShading prop has no effect on LayerMaterial

[marcelmusiol]

Adding flatShading prop to the LayerMaterial doesn't affect the shading.

Left: <meshMatcapMaterial matcap={matcap} flatShading />

Right: <LayerMaterial flatShading> <Matcap map={matcap} /> </LayerMaterial>

https://codesandbox.io/s/lamina-matcap-ho7v4z?file=/src/App.js