Serve 11 cannot set symlinks to true in config.json

`serve@^11`  currently errors out when setting `symlinks: true`:

```
root@c3ee02fdad56:/app# serve --version
11.0.0
root@c3ee02fdad56:/app# serve -p 8000 -c ./serve.json
INFO: Discovered configuration in `./serve.json`
ERROR: The configuration you provided is wrong:
should NOT have additional properties
{"additionalProperty":"symlinks"}
```
