[dom] rename before() and after() of ChildNode (#134)

https://domspecwhatwgorg/#childnode

I really dislike those method names There must be something better (Afaik they aren't shipping in any browser yet)
How about:
fitBefore
pushBefore

Sorry for ruining your sunday

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/dom/issues/134