it's complainedRecipients (even though complaintRecipients does seem more natural

Documented in http://docs.aws.amazon.com/ses/latest/DeveloperGuide/notification-examples.html, or a live example in stage:

```
{
  "notificationType":"Complaint",
  "complaint": {
    "complainedRecipients": [
      {
        "emailAddress":"complaint@simulator.amazonses.com"
      }
    ],
    "complaintFeedbackType":"abuse",
    "userAgent":"Amazon SES Mailbox Simulator",
    "timestamp":"2014-04-16T01:58:37.000Z",
    "feedbackId":"000001456841db3d-a0047bb6-c50a-11e3-8caf-ef48d5bebf3b-000000"
  },
  "mail":{
    "timestamp":"2014-04-16T01:58:36.000Z",
    "source":"verifications@stage.mozaws.net",
    "messageId":"000001456841d782-87c0ddad-b41c-49fd-ba1f-43c8d453f4aa-000000",
    "destination":["complaint@simulator.amazonses.com"]
  }
}
```