Fix closing list item tag (<li> -> </li>)

I think that this should have been a closing tag, not another opening tag.

Thanks for the wonderful sample site and theme!

_includes/feedback.html

@@ -10,4 +10,4 @@
 {% else %}
   <a class="email" title="Submit feedback" href="#" onclick="javascript:window.location='mailto:{{site.feedback_email}}?subject={{site.feedback_subject_line}} feedback&body=I have some feedback about the {{page.title}} page: ' + window.location.href;"><i class="fa fa-envelope-o"></i> {{feedback_text}}</a>
 {% endif %}
-<li>
+</li>