Fixed missing li closing tag

Author: aegilops

javascript/ql/src/Security/CWE-693/InsecureHelmet.qhelp

@@ -65,6 +65,7 @@
         </li>
         <li>
             <a href="https://developer.mozilla.org/en-US/docs/Web/Security#protect_against_clickjacking">Protect against clickjacking | MDN</a>
+        </li>
 
     </references>
 </qhelp>