After deploying the server to Zeit unable to perform first query from the tutorial.

After setting up the client and writing first query from part 5 of the tutorial, query isn't performed against deployed service:
```
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://server-ik661tevx.now.sh/graphql. (Reason: CORS preflight channel did not succeed)
```

从教程的第 5 部分开始，重现对已部署 GraphQL endpoint 的第一次查询。检查失败的 CORS 预检请求和服务器的部署配置；当教程客户端能够对已部署的服务执行第一次查询时，即表示完成。

由索引模型根据 Issue 内容生成。