DocumentFragment appending doesn't update children

[treshugart]

When you have a document fragment and append it to another node, the children of the document fragment still report that the parentNode is the fragment.

Test case:

const frag = document.createDocumentFragment();
const ch1 = document.createElement('div');

frag.appendChild(ch1);
target.appendChild(frag);
expect(ch1.parentNode).to.equal(target);