relabelNodes doesn't update the graph

Hi,

I could draw graph as I expected, and I now want to update the node without deleting the node.

firstly, I want to use `relabelNodes `, the label of the node changed but not reflected in the graph.
```
G.nodes()
Array [ old1", "old2" ]
```
```
var mapping = {"old1": "new1"};
var H = jsnx.relabelNodes(G, mapping, false)
```
```
G.nodes()
Array [ new1", "old2" ]
```
The label seems to be updated, but the actual label doesn't change, it only changes with following
```
jsnx.draw(G)
```
but I don't want to redraw everything, just want to update the single label.
It would be very appreciated if someone can correct me.