[WICG/webcomponents] Fix css-modules-v1-explainer.md (#932)

- Add missing `assert`s.
- Consistently use double quotes. 
- Add leading dot to import.
You can view, comment on, or merge this pull request online at:

  https://github.com/WICG/webcomponents/pull/932

-- Commit Summary --

  * Update css-modules-v1-explainer.md

-- File Changes --

    M proposals/css-modules-v1-explainer.md (4)

-- Patch Links --

https://github.com/WICG/webcomponents/pull/932.patch
https://github.com/WICG/webcomponents/pull/932.diff

-- 
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/WICG/webcomponents/pull/932