Wrong param name of the utils function

Why you named param - `getNodeKey`? definitely, it is not node key, it is INDEX of the path! I spent 2 hours for figured out why it does not work then I went to the source code and seen that it is the index.
Should be `getNodeKey: (item) => item.treeIndex,` but not getNodeKey: (item) => item.node.key,

```js
changeNodeAtPath({
treeData,
path,
newNode,
getNodeKey // get path index but not node key
})
```