[webcomponents] fixed code examples (#27)

fixes https://www.w3.org/Bugs/Public/show_bug.cgi?id=27545 and
https://www.w3.org/Bugs/Public/show_bug.cgi?id=27546
You can merge this Pull Request by running:

  git pull https://github.com/stevefaulkner/webcomponents gh-pages

Or you can view, comment on it, or merge it online at:

  https://github.com/w3c/webcomponents/pull/27

-- Commit Summary --

  * fixed code examples

-- File Changes --

    M spec/custom/index.html (4)

-- Patch Links --

https://github.com/w3c/webcomponents/pull/27.patch
https://github.com/w3c/webcomponents/pull/27.diff

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https://github.com/w3c/webcomponents/pull/27