JS: change notes for Koa improvements

Author: Esben Sparre Andreasen

change-notes/1.21/analysis-javascript.md

@@ -3,6 +3,7 @@
 ## General improvements
 
 * Support for the following frameworks and libraries has been improved:
+  - [koa](https://github.com/koajs/koa)
   - [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`, and a number of npm packages intcluding [`abab`](https://www.npmjs.com/package/abab), [`atob`](https://www.npmjs.com/package/atob), [`btoa`](https://www.npmjs.com/package/btoa), [`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).