Better constrcutor for ArcRotateCamera

dist/preview release/babylon.max.js

@@ -31196,7 +31196,7 @@ var BABYLON;
                 _this._target = BABYLON.Vector3.Zero();
             }
             else {
-                _this._target = target;
+                _this.setTarget(target);
             }
             _this.alpha = alpha;
             _this.beta = beta;

src/Cameras/babylon.arcRotateCamera.ts

@@ -213,7 +213,7 @@ module BABYLON {
             if (!target) {
                 this._target = Vector3.Zero();
             } else {
-                this._target = target;
+                this.setTarget(target);
             }
 
             this.alpha = alpha;