index: fix minor typo.

index.html

@@ -1841,7 +1841,7 @@ $("#multiselect").multiselect('dataprovider', data);
 				<h1><a id="additional-styling"></a>Additional Styling</h1>
 			</div>
 			<p>
-                For additionaly styling of the multiselect button the CSS class <code>multiselect</code> can be used.
+                For additional styling of the multiselect button, the CSS class <code>multiselect</code> can be used.
             </p>
 			<style media="screen" type="text/css">
 			    .add-styling-1 .multiselect {