[bug] API rate limit exceeded for server

[zhicheng-ning]

在 #12 中设置每日凌晨 5 点更新 repo statistic 数据后，在服务器中的日志中发现 API 速率超过限制，查看 GitHub API 文档后发现，普通的授权 token 每小时只能发起 5000 次请求。因此在每小时的请求次数耗尽后，该小时内无法再进行请求。

situation：

{
"message": "API rate limit exceeded for 219.78.228.97. (But here's the good news: Authenticated requests get a higher rate limit. Check out the documentation for more details.)",
"documentation_url": "https://docs.github.com/rest/overview/resources-in-the-rest-api#rate-limiting"
}

reason：

User-to-server requests are limited to 5,000 requests per hour and per authenticated user. All requests from OAuth applications authorized by a user or a personal access token owned by the user, and requests authenticated with any of the user's authentication credentials, share the same quota of 5,000 requests per hour for that user.

[zhicheng-ning]

考虑对 token 进行池化，维护一个 GitHub API 的 token 池

[zhicheng-ning]

目前的解决方式是通过配置文件将多个 token 注入到代码中的 token 列表，在进行请求的时候通过轮询顺序从 token 列表中取一个 token 发起请求