TS: Clean up

examples/jsm/loaders/3MFLoader.d.ts

@@ -12,4 +12,5 @@ export class ThreeMFLoader {
   load(url: string, onLoad: (object: Group) => void, onProgress?: (event: ProgressEvent) => void, onError?: (event: ErrorEvent) => void): void;
   setPath(value: string): this;
   parse(data: ArrayBuffer): Group;
+  addExtension(extension: object):void
 }