Upgrade outdated koa-convert dependency to ^2.0.0
`koa` depends on `koa-convert@1.2.0` which depends on `koa-compose@3.2.1` which depends on `any-promise`.

`any-promise` is very old (last release 5 years ago) and uses dynamic requires, which break bundlers like esbuild

```
node_modules/any-promise/register.js:24:14: warning: This call to "require" will not be bundled because the argument is not a string literal (surround with a try/catch to silence this warning)
```
`koa-convert@2.0.0` depends on `koa-compose@4.1.0` which has the dependency to `any-promise` removed. Because `koa` has a already a direct dependency to `koa-compose@4.1.0` (see [here](https://github.com/koajs/koa/blob/master/package.json#L49)), I hope it is safe to upgrade the dependency to `koa-convert`
