[dom] Use IDL link syntax in NonElementParentNode & ParentNode headings (#175)

For uniformity with all the other "Interface `Foo`" headings.
You can view, comment on, or merge this pull request online at:

  https://github.com/whatwg/dom/pull/175

-- Commit Summary --

  * Use IDL link syntax in NonElementParentNode & ParentNode headings for uniformity

-- File Changes --

    M dom.bs (4)

-- Patch Links --

https://github.com/whatwg/dom/pull/175.patch
https://github.com/whatwg/dom/pull/175.diff

---
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/dom/pull/175