Fix merge reference for ‘none’ scope

Author: pat

lib/thinking_sphinx/active_record/base.rb

@@ -59,7 +59,7 @@ def sphinx_search_for_ids(query = nil, options = {})
     end
 
     def sphinx_search_none
-      merge ThinkingSphinx.search, nil, none: true
+      merge_search ThinkingSphinx.search, nil, none: true
     end
 
     private