[plugins.json] Add cocoapods-delete-scheme

[lifely]

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

{
  "gem": "cocoapods-delete-scheme",
  "name": "CocoaPods Delete Scheme",
  "author": "Julien Di Marco",
  "url": "https://github.com/tillersystems/cocoapods-delete-scheme",
  "description": "A longer description of cocoapods-delete-scheme."
}