Internet Explorer requires Event polyfill

[nerdstep]

Internet Explorer breaks due to usage of the new Event constructor.

It works fine after adding a polyfill, but it was somewhat difficult to track this issue down since the error appears as originating in react-dom, and at least with a Create React App bootstrapped app, you can't easily test IE in development.

So testing the production build you get this useful error:

SCRIPT445: Object doesn't support this action
react-dom.production.min.js (169,13)

Initially I was trying to figure out why Babel/core-js wasn't polyfilling this but it seems they're not focused on DOM related APIs.

Anyway, I'm opening this issue because it might help others avoid similar grief trying to debug the problem. Perhaps a quick mention in the README would be warranted?

[quantizor]

Ooh interesting. Thanks for surfacing this! Would you be interested in doing a readme PR?

[nerdstep]

Sure thing!

As a point of further discussion, it might be more "correct" to use the CustomEvent API instead of Event.

Either way, both require a polyfill to support IE, though it is fairly minimal.