message: include credentials when fetching schema
diff: @@ -335,6 +335,7 @@ export class Playground extends React.PureComponent<Props & DocsState, State> {
  fetchSchema(endpointUrl: string, headers: any = {}) {
  return fetch(endpointUrl, {
  method: 'post',
  + credentials: 'include',
  headers: {
  'Content-Type': 'application/json',
  'X-Apollo-Tracing': '1',
  