docs: Fix link to main page
<para>This document is the API reference for the Graphene library.</para>
<para>
The latest version of Graphene, as well as the latest version of
- this API reference, is <ulink role="online-location" url="http://ebassi.github.com/graphene">available online</ulink>.
+ this API reference, is <ulink role="online-location" url="http://ebassi.github.io/graphene">available online</ulink>.
</para>
</releaseinfo>
</bookinfo>
