Update livedb-mongo to 0.2.x

There's an issue with current DerbyJS, and livedb-mongo 0.1.x.

It returns an error:

```
Error: Missing or invalid snapshot db
```

The fix is to upgrade livedb-mongo to the latest version.
Merge pull request #1 from victorhooi/master

Update livedb-mongo to 0.2.x