[plugins.json] Add cocoapods-mexdups

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"
}
```

Open plugins.json and compare the requested object with nearby plugin entries to confirm the repository’s formatting. Add the cocoapods-mexdups entry, validate that the JSON remains valid, and confirm the plugin appears in the catalog.

Written by the indexing model from the issue text.