[w3c/webcomponents] Fix template instantiation examples (#694)

Currently the JS object input doesn't match the desired output, and the syntax for `Element.setAttribute` was incorrect.

Also some minor nits in regard of backticks & trailing whitespace.
You can view, comment on, or merge this pull request online at:

  https://github.com/w3c/webcomponents/pull/694

-- Commit Summary --

  * Fix template instantiation examples

-- File Changes --

    M proposals/Template-Instantiation.md (14)

-- Patch Links --

https://github.com/w3c/webcomponents/pull/694.patch
https://github.com/w3c/webcomponents/pull/694.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/w3c/webcomponents/pull/694