IE 11 compatibility

[roman]

Hi, I'm trying to have cancellable fetch work in IE 11

I followed this chain of polyfills:
whatwg-fetch -> yet-another-abortcontroller-polyfill -> event-target-polyfill

I know that this package states possible support for IE 11, but unfortunately it doesn't work because Event constructor is defined, but throws with Object doesn't support this action. (At least in IE 11 on Windows 10 VM, that Microsoft provides, I haven't tested on older versions)

It seems to me, that the required change is pretty minimal, we only need to add another check for Event construction somewhere here