Upgrade examples to jQuery 3

[mgol]

Currently our examples use the really, really old jQuery 1.10.2 (it's over 3 years old). We should update them to jQuery 3 (currently 3.1.0). This means we will have to remove examples using removed APIs but I think we should do that anyway; such entries should be short and mostly focus on what to switch to, we shouldn't making it easier for people to use deprecated APIs.

The jQuery used in examples is included here: https://github.com/jquery/api.jquery.com/blob/a6f6b37/entries2html.xsl#L15.

[mgol]

Note that the jQuery used by examples is a different one to the one used by our sites; the latter is managed globally in the jquery-wp-content repo, here: https://github.com/jquery/api.jquery.com/blob/a6f6b37/entries2html.xsl#L15

[mgol]

The issue about upgrading jQuery on our sites is here: jquery/jquery-wp-content#400

cc @dmethvin @timmywil

[mgol]

PR: #1148