Redundant role="navigation" on <nav>s

plus one example that still used the old <div role="navigation"> and a
fix-up of the callout as per
https://github.com/twbs/bootstrap/issues/15109

docs/examples/justified-nav/index.html

@@ -33,7 +33,7 @@
 
       <div class="masthead">
         <h3 class="text-muted">Project name</h3>
-        <div role="navigation">
+        <nav>
           <ul class="nav nav-justified">
             <li class="active"><a href="#">Home</a></li>
             <li><a href="#">Projects</a></li>
@@ -42,7 +42,7 @@
             <li><a href="#">About</a></li>
             <li><a href="#">Contact</a></li>
           </ul>
-        </div>
+        </nav>
       </div>
 
       <!-- Jumbotron -->