winston-cloudwatch: Program does not terminate

I’ve tried using the code from the readme. The message does appear in my AWS CloudWatch console, but the program does not terminate. I am using nodejs 6.2.1.

const config = require('./config.json')
const winston = require('winston')
const WinstonCloudWatch = require('winston-cloudwatch')
const moment = require('moment')

winston.add(WinstonCloudWatch, {
  logGroupName: config.cloudWatchLogGroup,
  logStreamName: config.cloudWatchStream,
  awsRegion: config.region
});

winston.info('this is a message sent at ' + moment().format('YYYY-MM-DD-hhmm') + ' from winston-cloudwatch.js');

Thanks for any assistance.