Page find method signature should be corrected

Made a simple change to a method signature to address a stack trace when trying to generate a gollum site (with gollum version 2.4.11 installed).

The commit aims to resolve https://github.com/dreverri/gollum-site/issues/25.

    commit 963c2e9
    Author: Marcus Pemer <marcus@iteego.com>
    Date:   Fri Jan 25 09:51:19 2013 +0100
    
        Matched signature of find method with that of the parent class from gollum 2.4.11.
    
        The mismatch in signature caused a stacktrace when trying to generate a site.
    
    :100644 100644 357f9ba... c72584d... M  lib/gollum-site/page.rb