message: Fix up subscription API in using-subscriptions example
diff: @@ -19,12 +19,11 @@ const subscriptionClient = new SubscriptionClient(
  const client = createClient({
  url: 'http://localhost:4000/graphql',
  - subscriptionHandler: operation => subscriptionClient.request(operation),
  exchanges: [
  debugExchange,
  cacheExchange,
  fetchExchange,
  - subscriptionExchange,
  + subscriptionExchange(operation => subscriptionClient.request(operation)),
  ],
  });
  