Google broke old site-search method, this fixes it

.themes/classic/source/_includes/navigation.html

@@ -7,7 +7,7 @@
   {% if site.simple_search %}
 <form action="{{ site.simple_search }}" method="get">
   <fieldset role="search">
-    <input type="hidden" name="q" value="site:{{ site.url | shorthand_url }}" />
+    <input type="hidden" name="sitesearch" value="{{ site.url | shorthand_url }}">
     <input class="search" type="text" name="q" results="0" placeholder="Search"/>
   </fieldset>
 </form>