Rotating-file stream prevent process from exiting.

Related: #73 

If I `bunyan.createLogger` with a `type: "rotating-file"`, my process will not exits.

I've tried the solution in #73 but it does not work and my CLI program stays running even though it doesn't do anything.

Removing the rotating-file logger causes my very trivial program to exit cleanly.

Is there a way to force the logger to close all streams?

This is also very problematic in tests as having a component using the rotating-file logger means the test will not cleanup properly or the test runner may not exit and hangs the CI :/