Bump koa from 2.8.1 to 2.9.0

Bumps [koa](https://github.com/koajs/koa) from 2.8.1 to 2.9.0.
- [Release notes](https://github.com/koajs/koa/releases)
- [Changelog](https://github.com/koajs/koa/blob/master/History.md)
- [Commits](koajs/koa@2.8.1...2.9.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -27,7 +27,7 @@
     "express": "^4.17.1",
     "human-readable-numbers": "^0.9.5",
     "ioredis": "^4.14.0",
-    "koa": "^2.8.1",
+    "koa": "^2.9.0",
     "koa-router": "^7.4.0",
     "koa-send": "^5.0.0",
     "mem": "^5.1.1",