fix lag reporting

Currently lag gets reported like:

```
2014-03-23T05:46:10.842782+00:00 app[bot.1]: 2014/03/23 05:46:10 Lag: 387653h46m10.842731972ss
```

Which seems to be because `event.Raw` is being passed into `ParseInt`. This patch changes the lag calculation to use `event.Arguments[1]` and also removes the trailing "s" from the output:

```
2014-03-23T06:03:32.646673+00:00 app[bot.1]: 2014/03/23 06:03:32 Lag: 34.870266ms
```