Fix typo in slide

class4.html

@@ -70,7 +70,7 @@ <h3>Warning</h3>
           <h3>What is an API?</h3>
           <ul>
             <li class = "fragment"><span class = "yellow">A</span>pplication <span class = "yellow">P</span>rogramming <span class = "yellow">I</span>nterface</li>
-            <li class = "fragment">Data structure and rules for accessing a web-based appllication</li>
+            <li class = "fragment">Data structure and rules for accessing a web-based application</li>
             <li class = "fragment">How we can access information from sites that are not our own (Twitter, Meetup, Facebook, Foursquare)</li>
           </ul>
         </section>