koa response type 'application/xml'
```
import Koa from 'koa';
import Router from 'koa-router';

export default async function(config: Configuration) {

  const router = new Router();

  router.post('/abcdefg', async ({
    request,
    response
  }) => {

    response.body = '<Settlement><success_code>0</success_code></Settlement>';
    response.set('Content-Type', 'application/xml');
    response.type = 'application/xml';
    response.status = 200;
  });

  return new Koa()
    .use(router.routes())
    .use(router.allowedMethods());
}
```

returns `{}` where I expect `<Settlement><success_code>0</success_code></Settlement>`