[plugins.json] Add cocoapods-mexdups

[ashine]

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

{
  "gem": "cocoapods-mexdups",
  "name": "CocoaPods Mexdups",
  "author": "ashine",
  "url": "https://github.com/JHshine/cocoapods-mexdups",
  "description": "根据pod组件移除壳工程中的重复文件,先输入pod文件夹，再输入工程文件夹"
}