[webcomponents] minor editorial fixes. (#346)

Trivial corrections.
You can view, comment on, or merge this pull request online at:

  https://github.com/w3c/webcomponents/pull/346

-- Commit Summary --

  * minor editorial fixes.

-- File Changes --

    M proposals/Shadow-DOM-Cascade-Order-in-v1.md (10)

-- Patch Links --

https://github.com/w3c/webcomponents/pull/346.patch
https://github.com/w3c/webcomponents/pull/346.diff

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https://github.com/w3c/webcomponents/pull/346