Order site map entries alphabetically

The pages in the site map are currently ordered by date. This doesn't make
much sense in the list. Order alphabetically instead to make it a bit
clearer.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

themes/beautifulhugo/layouts/partials/nav.html

@@ -84,7 +84,7 @@
                {{ if .InSection $section }}id="sidebar-focus"{{end}}>{{ .Title }}</a>
             <div class="sidebar-pages">
               <ul>
-                {{ range .Pages }}
+                {{ range .Pages.ByTitle }}
                   <li class="sidebar-page">
                     <a href="{{ .URL | relLangURL }}">{{ .Name }}</a>
                   </li>