Error.captureStackTrace is not a function in firefox

Erraneous code:

https://github.com/trentm/node-bunyan/blob/master/lib/bunyan.js#L143

I didn't take the time to check out what captureStackTrace does exactly to find if any other code depended on it. In my fork I'm just wrapping it which seems to work fine:

if (typeof Error.captureStackTrace === 'function') {
  // capture the stack
}

Again, firefox 35.0.1 on ubuntu 14.10