Fix bug: preview was always true

lib/parsers/parser_front_end.rb

@@ -46,7 +46,7 @@ module ParserFrontEnd
         # ret << "&category_id=#{page.category}" if page[:category]
         ret << "&category_id=#{params[:category_id]}" if !params[:category_id].blank?
         ret << "&tag_id=#{params[:tag_id]}" if !params[:tag_id].blank?
-        ret << "&preview=true" if preview
+        ret << "&preview=true" if preview.eql?('true')
         ret << "'></div>"
       else
         part = page.page_parts.detect{ |p| p.name.to_s == content['name'].to_s } rescue nil