Update BufferGeometryUtils.d.ts

examples/jsm/utils/BufferGeometryUtils.d.ts

 import { BufferAttribute, BufferGeometry } from '../../../src/Three';
 
 export namespace BufferGeometryUtils {
-    export function mergeBufferGeometries(geometries: BufferGeometry[], useGroups: boolean): BufferGeometry;
+    export function mergeBufferGeometries(geometries: BufferGeometry[], useGroups?: boolean): BufferGeometry;
     export function computeTangents(geometry: BufferGeometry): null;
     export function mergeBufferAttributes(attributes: BufferAttribute[]): BufferAttribute;
 }