Fix a typo problem

Author: afshinm

example/hello-world/index.html

@@ -33,7 +33,7 @@ <h3 class="muted">Intro.js</h3>
       <hr>
 
       <div class="jumbotron">
-        <h1 data-step="1" data-intro="This is a tooltip!">Basic Usage</span></h1>
+        <h1 data-step="1" data-intro="This is a tooltip!">Basic Usage</h1>
         <p class="lead" data-step="4" data-intro="Another step.">This is the basic usage of IntroJs, with <code>data-step</code> and <code>data-intro</code> attributes.</p>
         <a class="btn btn-large btn-success" href="javascript:void(0);" onclick="javascript:introJs().start();">Show me how</a>
       </div>