Markup component will not update if the mapping of custom elements change

When using the option to add a map of custom elements the component will not update if said mapping changes.

I think the problem might be here:
https://github.com/developit/preact-markup/blob/034c4c6e13029d94db57c8a565191a03b214eb83/src/index.js#L11-L14

Now I don't know if this is intended behaviour or just a oversight.