支持自定义GitHub API代理

[Muska-Ami]

如题，可将 proxy 选项变更为

{
  // ...
  "proxy": {
    "cors-anywhere": "https://cors-anywhere.1l1.icu/github.com/login/oauth/access_token"
    "api": "https://api-gh.1l1.icu"
  } // By giving a demo, please see https://blog.1l1.icu
}