Use fallthrough and forward plugin did not take effect

when i use the configuration, i can not resovler node name.

```
xxx:53 {
  kubeapi
  kubenodes . {
    ttl 30
    fallthrough .
  }
  forward . xxx:53 {
    prefer_udp
  }
  errors
  cache 30
}
```

but if not use fallthrough and forward, it can do it