MaxListenersExceededWarning caused by Sandbox.js

Created by: zlafil

Bull version: 3.5.2

It seems that sandbox.js never removes the listener for the exit event. This causes the MaxListenersExceededWarning to be shown in Node.

https://github.com/OptimalBits/bull/blob/develop/lib/process/sandbox.js#L36

Example in TypeScript

 const queue = new Bull("Queue", { redis: { port: Config.config.redisPort, host: Config.config.redisHost } });
  queue.process(1, "pathToWorker.js");
  for (let i = 0; i < 12; i++) {
    queue.add("");
  }

Adding

child.removeListener('exit');

before this line https://github.com/OptimalBits/bull/blob/develop/lib/process/sandbox.js#L41 seems to solve the problem