Added EventType: "desktop_notification"

[sgr-ksmt]

• Add EventType "desktop_notification".

SlackKit currently output error log when received as below:

{
  "content": "user: @bot abcdef",
  "event_ts": 1484119301.624465,
  "launchUri": "slack://channel?id=xxxxx&message=1484119301000012&team=xxxxx",
  "subtitle": "#xxxxx",
  "ssbFilename": "knock_brush.mp3",
  "title": "xxxxx",
  "channel": "xxxxx",
  "avatarImage": "https://avatars.slack-edge.com/xxxxx.png",
  "type": "desktop_notification",
  "imageUri": null,
  "msg": 1484119301.000012
}

then output log:

Error: SlackKit.Event

[pvzig]

Thanks for the PR!

Since this isn't officially supported by Slack I don't think I want to specifically add it as an event type but unsupported events shouldn't be logged as errors either.

Fixed here.