Use protocol-relative URL for html5shim in examples

Created by: cvrebert

The included examples currently load the shim using:

    <script src="http://html5shim.googlecode.com/svn/trunk/html5.js"></script>

The URL should instead be protocol-relative so that the examples are copy-paste-ready-to-go for HTTPS sites, like in the shim's own example:

    <script src="//html5shim.googlecode.com/svn/trunk/html5.js"></script>