Bump koa from 2.5.0 to 2.15.4 in /frameworks/JavaScript/koa

Bumps [koa](https://github.com/koajs/koa) from 2.5.0 to 2.15.4.
- [Release notes](https://github.com/koajs/koa/releases)
- [Changelog](https://github.com/koajs/koa/blob/2.15.4/History.md)
- [Commits](koajs/koa@2.5.0...2.15.4)

---
updated-dependencies:
- dependency-name: koa
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

frameworks/JavaScript/koa/package.json

@@ -7,7 +7,7 @@
   "dependencies": {
     "bluebird": "3.5.1",
     "handlebars": "4.3.0",
-    "koa": "2.5.0",
+    "koa": "2.15.4",
     "koa-bodyparser": "4.2.0",
     "koa-hbs": "1.0.0",
     "koa-router": "7.4.0",