Fix attachToBone process

src/Bones/skeleton.ts

@@ -407,6 +407,7 @@ export class Skeleton implements IAnimatable {
 
         for (var index = 0; index < this.bones.length; index++) {
             var bone = this.bones[index];
+            bone._childUpdateId++;
             var parentBone = bone.getParent();
 
             if (parentBone) {

src/node.ts

@@ -125,7 +125,8 @@ export class Node implements IBehaviorAware<Node> {
     /** @hidden */
     public _currentRenderId = -1;
     private _parentUpdateId = -1;
-    protected _childUpdateId = -1;
+    /** @hidden */
+    public _childUpdateId = -1;
 
     /** @hidden */
     public _waitingParentId: Nullable<string>;