add nav class to tabs in javascript demo

docs/javascript.html

@@ -479,7 +479,8 @@ $('a[data-toggle="tab"]').on('shown', function (e) {
   e.relatedTarget // previous tab
 })</pre>
           <h3>Demo</h3>
-          <ul id="tab" class="tabs">
+
+          <ul id="tab" class="nav tabs">
             <li class="active"><a href="#home" data-toggle="tab">Home</a></li>
             <li><a href="#profile" data-toggle="tab">Profile</a></li>
             <li><a href="#messages" data-toggle="tab">Messages</a></li>