fixed JumpTo bug with wrong _delta position

Every _cc.JumpTo.startWithTarget(target)_ call changes _delta position.

Reproduce:
open _myApp.js_ in template;
add
```javascript
this.sprite.runAction(
    cc.RepeatForever.create(
        cc.JumpTo.create(1, cc.p(size.width / 2, size.height / 2), 100, 1)
    )
);
```
at the end of _init()_ function;

Expected result: cocos sprite jumps on the same position;
Result: cocos sprite jumps off screen then returns.