Running on Heroku

FYI, to get this running on Heroku I had to make a couple of tweaks:

config.js, the `process.env.PORT`

```
outgoingWebhookServer: {
  port: Number(process.env.PORT || 5000),
```

lib/slack.js, the `0.0.0.0`

```
var server = new Hapi.Server('0.0.0.0', config.slack.outgoingWebhookServer.port, {
```
