[plugins.json] Add cocoapods-proxy

[tuyw]

Please add the following entry to the plugins.json file:

{
  "gem": "cocoapods-proxy",
  "name": "CocoaPods Proxy",
  "author": "tuyw",
  "url": "https://github.com/tuyuwang/cocoapods-proxy",
  "description": "使用代理进行替换pod install时对仓库的 git clone."
}