[plugins.json] Add cocoapods-packing-cubes

[ruzhuxiaogu]

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

{
  "gem": "cocoapods-packing-cubes",
  "name": "CocoaPods Packing Cubes",
  "author": "tingdongli",
  "url": "https://github.com/segiddins/cocoapods-packing-cubes",
  "description": "A CocoaPods plugin that allows customizing how individual pods are packaged and linked."
}

[Samuel Giddins]

Packing cubes should no longer be necessary with the latest CocoaPods releases.