error: better handle uncaught worker exceptions

Hi! This PR about https://github.com/nodules/luster/blob/master/lib/worker.js#L57 workerDomain 'error' handler.
First, I think there are no reason to log error and then exit process with code 1. It is equal to throwing an exception.
Also there is an opinion that domain should consider special 'uncaughtException' event handler