Left/right/depth attributes not updated on the record after update

NestedSetsBehavior will set the `lft`, `rgt`, and `depth` attributes on the record when it’s a new record, but it won’t update those attributes after performing an operation on an existing record.

Example:

```php
$a->prependTo($b);
echo $a->lft;
```

I would expect that to output the new `lft` attribute value, but it will output the old one.