GitHub GraphQL API does not follow GraphQL spec for some errors

If we try to use the GraphQL endpoint without a token, we receive the following response:

{'message': 'This endpoint requires you to be authenticated.', 'documentation_url': ''}

If we use an invalid token, we receive:

{'message': 'Bad credentials', 'documentation_url': ''}

In both cases, the answer does not follow the GraphQL spec which says:

If the operation encountered any errors, the response map must contain an entry with key errors

This can causes problems for GraphQL clients which are conforming to the spec and do not recognize the answer.
See issue python gql #149