[dom] Node.replaceChild() doesn't correctly queue mutation records (#59)

Step 13 states that the mutation record's previous sibling should be `child`'s previous sibling, but `child` was removed from its parent on step 10. There should be a step between 9 and 10 where its previous sibling is bound to a variable and reused in step 13.

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/dom/issues/59