WebGLRenderLists.d.ts: add groupOrder to RenderItem interface

src/renderers/webgl/WebGLRenderLists.d.ts

@@ -15,6 +15,7 @@ export interface RenderItem {
   geometry: Geometry | BufferGeometry;
   material: Material;
   program: WebGLProgram;
+	groupOrder: number;
   renderOrder: number;
   z: number;
   group: Group;