JavaScript: Add change note.

Author: Max Schaefer

change-notes/1.21/analysis-javascript.md

@@ -5,6 +5,9 @@
 * Support for the following frameworks and libraries has been improved:
   - [socket.io](http://socket.io)
 
+* The security queries now track data flow through Base64 decoders such as the Node.js `Buffer` class, the DOM function `atob`, as well as the npm packages [`base-64`](https://www.npmjs.com/package/base-64), [`js-base64`](https://www.npmjs.com/package/js-base64), [`Base64.js`](https://www.npmjs.com/package/Base64) and [`base64-js`](https://www.npmjs.com/package/base64-js).
+
+
 ## New queries
 
 | **Query**                                     | **Tags**                                             | **Purpose**                                                                                                                                                                 |