__typename-rels is not a valid inc parameter for the artist resource.

The below query

```graphql
query Artist {
node(id: "QXJ0aXN0OjMyM2VkOTc0LThiZjYtNGY1NC05NTI1LWI3NzRhNjU5ZjgwNQ==") {
... on Artist {
relationships {
__typename
}
}
}
}
```

when used on https://graphbrainz.herokuapp.com/ fails with

```json
{
"errors": [
{
"message": "__typename-rels is not a valid inc parameter for the artist resource.",
"locations": [
{
"line": 4,
"column": 7
}
],
"path": [
"node",
"relationships"
]
}
],
"data": {
"node": {
"relationships": null
}
}
}
```
The problem seems to come from the `__typename` meta-field that is not correctly understood: https://spec.graphql.org/draft/#sec-Type-Name-Introspection