Update index.html

Updated text in the jumbotron container to reflect the Bootstrap 3 change from 'hero unit' to 'jumbotron'.

examples/theme/index.html

@@ -64,7 +64,7 @@
       <!-- Main jumbotron for a primary marketing message or call to action -->
       <div class="jumbotron">
         <h1>Hello, world!</h1>
-        <p>This is a template for a simple marketing or informational website. It includes a large callout called the hero unit and three supporting pieces of content. Use it as a starting point to create something more unique.</p>
+        <p>This is a template for a simple marketing or informational website. It includes a large callout called a jumbotron and three supporting pieces of content. Use it as a starting point to create something more unique.</p>
         <p><a href="#" class="btn btn-primary btn-lg" role="button">Learn more &raquo;</a></p>
       </div>