Typo fix.

Author: Pearl Chen

index.html

@@ -234,7 +234,7 @@ <h2>Good file naming habits</h2>
             (The browswer will interpret it as <code>business%20hours.html</code>)</span>
         </li>
         <li>
-          For the same reason, avoid symboles like <code># &amp; *</code> in your file name.
+          For the same reason, avoid symbols like <code># &amp; *</code> in your file name.
         </li>
         <li>
           Keep your file names concise, yet meaningful.<br />