Support shadowDOM elements

[tusharmath]

Closest is being used by https://github.com/zenorocha/delegate which I am using in my project. Unfortunately delegate doesn't work for shadowDOM elements because of the strict checking closest is doing with the global document object.

[ryanve]

Seems like a good idea to me but is there a simpler way maybe to do the check? Like comparing nodeType? It says here that shadow root is 11

while (parent && parent.nodeType === 1)

[ForbesLindesay]

I agree with @ryanve this doesn't look like a very clean approach.

[heartyoh]

Closest is being used by https://github.com/bpmn-io/min-dom.

https://github.com/bpmn-io/min-dom/issues/5 is also related.