chore(deps): bump koa from 2.14.2 to 2.15.4

Bumps [koa](https://github.com/koajs/koa) from 2.14.2 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@2.14.2...2.15.4)

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

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

Author: dependabot[bot]

package-lock.json

@@ -67,7 +67,7 @@
     "get-stream": "^6.0.0",
     "is-stream": "^2.0.0",
     "isbinaryfile": "^5.0.0",
-    "koa": "^2.13.0",
+    "koa": "^2.15.4",
     "koa-etag": "^4.0.0",
     "koa-send": "^5.0.1",
     "koa-static": "^5.0.0",