Another Typo

Fixed another typo pointed out by panahi.

docs/scaffolding.html

@@ -611,7 +611,7 @@
         </tbody>
       </table>
       <h3>Test case</h3>
-      <p>Resize your browser or load on different devices to test the above clases.</p>
+      <p>Resize your browser or load on different devices to test the above classes.</p>
       <h4>Visible on...</h4>
       <ul class="responsive-utilities-test">
         <li>Phone<span class="visible-phone">&#10004; Phone</span></li>