[plugins.json] Add cocoapods-gollen

[Gollen]

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

{
  "gem": "cocoapods-gollen",
  "name": "CocoaPods Gollen",
  "author": "祥子",
  "url": "https://github.com/EXAMPLE/cocoapods-gollen",
  "description": "A longer description of cocoapods-gollen."
}

[Samuel Giddins]

"url": "https://github.com/EXAMPLE/cocoapods-gollen",

is still the example URL