Use safe stringify when serializing error msg

Using circular structure safe JSON serialization for error message. Doing this because I got this error at some point:
```
irc-factory/lib/api.js:20
		self.emit('uncaughtException', {message: JSON.stringify(err)});
		                                              ^
TypeError: Converting circular structure to JSON
    at Object.stringify (native)
    at process.<anonymous> (/Users/rodrigo/projs/irc-factory/lib/api.js:20:49)
    at process.EventEmitter.emit (events.js:117:20)
    at process._fatalException (node.js:272:26)
```