add Promise for UIAnimation.

Hello.
add Promise for UIAnimation.

Like this

```
　__weak typeof(self) weakSelf = self;
 dispatch_promise_on(dispatch_get_main_queue(),^{
        return [UIView promiseAnimationWithDuration:0.2
                                         animations:^{
            weakSelf.label1.x = 500;
            
        }];
    }).then(^(BOOL finished){
        return [UIView promiseAnimationWithDuration:0.2 animations:^{
             weakSelf.label2.y = 600;
            
        }];
    }).then(^(BOOL finished){
        return [UIView promiseAnimationWithDuration:0.2 animations:^{
            weakSelf.label3.y = -100;
            
        }];
        
    })
```
please check.

Appears to missing the `fulfiller()`