Add missing full stop.

Co-authored-by: Marcono1234 <[email protected]>

Author: lcartey

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

@@ -6,7 +6,7 @@
 <p>Using unsanitized untrusted data in an external API can cause a variety of security issues. This query reports 
 all external APIs which are used with untrusted data, along with how frequently the API is used, and how many 
 unique sources of untrusted data flow this API. This query is designed primarily to help identify which APIs 
-may be relevant for security analysis of this application</p>
+may be relevant for security analysis of this application.</p>
 
 <p>An external API is defined as a method call to a method which is not defined in the source code, not overridden 
 in the source code, and is not modeled as a taint step in the default taint library. External APIs may be from the