lib/plugins/aws/provider/awsProvider.js/AwsProvider/getStage
class AwsProvider:  getStage() {
    const defaultStage = 'dev';

    return _.get(this, 'options.stage')
      || _.get(this, 'serverless.config.stage')
      || _.get(this, 'serverless.service.provider.stage')
      || defaultStage;
  }