TS: Fix ShadowMaterial.d.ts.

src/materials/ShadowMaterial.d.ts

-import { ShaderMaterialParameters, ShaderMaterial } from './ShaderMaterial';
+import { Color } from './../math/Color';
+import { MaterialParameters, Material } from './Material';
 
-export class ShadowMaterial extends ShaderMaterial {
+export interface ShadowMaterialParameters extends MaterialParameters {
+	color?: Color | string | number;
+}
+
+export class ShadowMaterial extends Material {
+
+	constructor( parameters?: ShadowMaterialParameters );
 
-	constructor( parameters?: ShaderMaterialParameters );
+	color: Color;
 
 }