Add role="tablist" to .nav-pills in examples to improve accessibility

Follow-up to e9374c0609
Per https://github.com/paypal/bootstrap-accessibility-plugin/commit/f203dea4b6d17264d7b776f02feaeeaa386cc9b2
Credit: https://github.com/paypal/bootstrap-accessibility-plugin & @rohk

[skip sauce]

docs/examples/jumbotron-narrow/index.html

@@ -34,7 +34,7 @@
 
     <div class="container">
       <div class="header">
-        <ul class="nav nav-pills pull-right">
+        <ul class="nav nav-pills pull-right" role="tablist">
           <li class="active"><a href="#">Home</a></li>
           <li><a href="#">About</a></li>
           <li><a href="#">Contact</a></li>

docs/examples/theme/index.html

@@ -338,7 +338,7 @@
       <p>
         <a href="#">Inbox <span class="badge">42</span></a>
       </p>
-      <ul class="nav nav-pills">
+      <ul class="nav nav-pills" role="tablist">
         <li class="active"><a href="#">Home <span class="badge">42</span></a></li>
         <li><a href="#">Profile</a></li>
         <li><a href="#">Messages <span class="badge">3</span></a></li>
@@ -369,7 +369,7 @@
         <li><a href="#">Profile</a></li>
         <li><a href="#">Messages</a></li>
       </ul>
-      <ul class="nav nav-pills">
+      <ul class="nav nav-pills" role="tablist">
         <li class="active"><a href="#">Home</a></li>
         <li><a href="#">Profile</a></li>
         <li><a href="#">Messages</a></li>