updates hgroup example

live-examples/html-examples/content-sectioning/hgroup.html

@@ -1,5 +1,5 @@
 <hgroup>
     <h1>Calculus I</h1>
-    <h2>Fundamentals</h2>
+    <p>Fundamentals</p>
 </hgroup>
 <p>This course will start with a brief introduction about the limit of a function. Then we will describe how the idea of derivative emerges in the Physics and Geometry fields. After that, we will explain that the key to master calculus is &hellip;</p>