chore(deps-dev): bump @types/koa from 2.13.6 to 2.13.9 (#159)

Bumps [@types/koa](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/koa) from 2.13.6 to 2.13.9.
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits/HEAD/types/koa)

---
updated-dependencies:
- dependency-name: "@types/koa"
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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