Cookies not being used when fetching schema

[NSGReaper]

The credentials: 'include' directive is supposed to be in the options object itself, not headers.
Because of this cookies are not included in the schema fetch request.

https://github.com/graphcool/graphql-playground/blob/1cdf0baec1afb40066edc7a0520b4ba35410c897/packages/graphql-playground-react/src/components/Playground/SchemaFetcher.ts#L34