gqlgen doesn't the newish "repeatable" token on directives like graphql-java

**What happened?**
gqlgen failed at this line:
directive @key(fields: _FieldSet!) repeatable on OBJECT | INTERFACE
error I got: GraphQLError: Syntax Error: Expected "on", found Name "repeatable"


**What did you expect?**
It should support the new 'repeatable' token

**Minimal graphql.schema and models to reproduce**
directive @key(fields: _FieldSet!) repeatable on OBJECT | INTERFACE