BUG in set status = 200
in my router
```
router.get('/test', function (ctx, next) {
    ctx.status = 200;
});

```

test
`http://localhost:3000/api/test`

got 
```
{
  "statusCode": 404,
  "error": "Not Found",
  "message": "missing"
}
```

if I remove the middleware, everything is OK
