Update event handlers if they changed

[korommatyi]

The original code doesn't handle the case when the event handler changes on an update.

My use case:

• I have a chart on my page. A click on a bar selects the corresponding category, so the chart is updated, the selected bar becomes more prominent while the other bars become almost transparent.
• In this state, a click deselects the previously selected category, removing all the highlight effects.

Currently this is impossible since the click handler is not updated when a new one is provided in the props on update.

I haven't found any contribution guide, so let me know if there are some steps I should take before this can be merged.

[erbenpeter]

It seems #151 deals with similar issues. Have you checked that one?

[korommatyi]

Ah, indeed. I didn't check other PRs... I will close this in favor of #151. That one even has a test! 😄