update slack adapter

```
2014-12-09T07:26:05.532840+00:00 app[web.1]: hubot-slack@3.0.0 node_modules/hubot-slack
2014-12-09T07:26:05.532841+00:00 app[web.1]: └── slack-client@1.1.0 (log@1.4.0, coffee-script@1.6.3, ws@0.4.31)
2014-12-09T07:26:06.770417+00:00 app[web.1]: [Tue Dec 09 2014 16:26:06 GMT+0900 (JST)] ERROR v2 services token provided, please follow the upgrade instructions
```