Update a webhook

{
    "webhook": {
      "name": "My Hook",
      "url": "http://example.com/my-hook",
      "events": [
        "subscribe",
        "unsubscribe",
        "sent"
      ],
      "sources": [
        "public",
        "system"
      ]
    }
}

{
  "webhook": {
    "cdate": "2016-01-01T12:00:00-00:00",
    "listid": "0",
    "name": "My Hook",
    "url": "http://example.com/my-hook",
    "events": [
      "subscribe",
      "unsubscribe",
      "sent"
    ],
    "sources": [
      "public",
      "system"
    ],
    "links": [],
    "id": "1"
  }
}