doc: fix order of end tags of list after heading

Current html result of a list after heading is <div
class="signature"><ul>...</div></ul>. Correct it to <div
class="signature"><ul>...</ul></div>.

PR-URL: https://github.com/nodejs/node/pull/5874
Fixes: https://github.com/nodejs/node/issues/5873


Reviewed-By: Roman Reiss <me@silverwind.io>