resolve issue #87 in this branch

lib/scaffolding.less

@@ -81,20 +81,20 @@ body {
 }
 
 // Container (centered, fixed-width layouts)
-div.container {
+.container {
   width: 940px;
   margin: 0 auto;
 }
 
 // Fluid layouts (left aligned, with sidebar, min- & max-width content)
-div.container-fluid {
+.container-fluid {
   padding: 0 20px;
   .clearfix();
-  div.sidebar {
+  .sidebar {
     float: left;
     width: 220px;
   }
-  div.content {
+  .content {
     min-width: 700px;
     max-width: 1180px;
     margin-left: 240px;