Add missing </p> tag

Co-authored-by: Felicity Chapman <[email protected]>

Author: lcartey

java/ql/src/Security/CWE/CWE-020/ExternalAPIsUsedWithUntrustedData.qhelp

@@ -28,7 +28,7 @@ used as the qualifier to the method call.</p>
 </ul>
 
 <p>Otherwise, the result is likely uninteresting. Custom versions of this query can extend the <code>SafeExternalAPIMethod</code> 
-class to exclude known safe external APIs from future analysis.
+class to exclude known safe external APIs from future analysis.</p>
 
 </recommendation>
 <example>