[plugins.json] Add cocoapods-ipub

[Welkiner]

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

{
  "gem": "cocoapods-ipub",
  "name": "CocoaPods Ipub",
  "author": "welkiner",
  "url": "https://github.com/welkiner/cocoapods-ipub",
  "description": "make a distinction between internal dependency and external dependency."
}

[Welkiner]

#88 the pull-request

[Orta Therox]

This is in