TS: Fix inheritance of WebXRManager.

src/renderers/webxr/WebXRManager.d.ts

@@ -1,7 +1,8 @@
 import { Group } from '../../objects/Group';
 import { Camera } from '../../cameras/Camera';
+import { EventDispatcher } from '../../core/EventDispatcher';
 
-export class WebXRManager {
+export class WebXRManager extends EventDispatcher {
 
 	constructor( renderer: any, gl: WebGLRenderingContext );