[dom] Pull Request: Fix NodeIterator removing step

Joris-van-der-Wel has just submitted a new pull request for 
https://github.com/whatwg/dom:

== Fix NodeIterator removing step ==
https://dom.spec.whatwg.org/#interface-nodeiterator

> 4\. If __next__ __is not__ an inclusive ancestor of __root__, set 
the referenceNode attribute to next and terminate these steps. 

This should be:

> 4\. If __root__ __is__ an inclusive ancestor of __next__, set the 
referenceNode attribute to next and terminate these steps. 

Otherwise you will end up with the following node of the iterator's 
`root`. Firefox and Chrome seem to behave in line with this fix.

See https://github.com/whatwg/dom/pull/24