Added missing constructor in AnimationAction.d.ts

src/animation/AnimationAction.d.ts

 import { AnimationMixer } from './AnimationMixer';
 import { AnimationClip } from './AnimationClip';
 import { AnimationActionLoopStyles } from '../constants';
+import { Object3D } from '../core/Object3D';
 // Animation ////////////////////////////////////////////////////////////////////////////////////////
 
 export class AnimationAction {
 
+	constructor( mixer: AnimationMixer, clip: AnimationClip, localRoot?: Object3D );
+
 	loop: AnimationActionLoopStyles;
 	time: number;
 	timeScale: number;