message: fix async fetchOptions recipe
diff: @@ -33,7 +33,19 @@ If we add the above exchange before our `fetchExchange` our `fetchOptions` will
  ```js
  const client = createClient({
  url: 'http://yourUrl.dev/',
  - exchanges: [dedupExchange, cacheExchange, fetchOptionsExchange, fetchExchange],
  + exchanges: [
  + dedupExchange,
  + cacheExchange,
  + fetchOptionsExchange(async (fetchOptions: any) => {
  + return Promise.resolve({
  + ...fetchOptions,
  + headers: {
  + Authorization: 'Bearer mySuperToken',
  + },
  + });
  + }),
  + fetchExchange,
  + ],
  });
  ```
  