Add an option to get the id of an event

[Techcable]

All events start with an 'event id' like this:

  {
    "id": "2834753425",
    "type": "ForkEvent",
    "actor": {
      "id": 8795909,
      "login": "Prismarine",
      "gravatar_id": "",
      "url": "https://api.github.com/users/Prismarine",
      "avatar_url": "https://avatars.githubusercontent.com/u/8795909?"
    },
    "repo": {
      "id": 29747510,
      "name": "Techcable/mc-dev",
      "url": "https://api.github.com/repos/Techcable/mc-dev"
    },

Could you please add a method to get the event id from the api?

[kohsuke]

Fixed toward 1.72