lib/plugins/aws/rollbackFunction/index.js/AwsRollbackFunction/constructor
class AwsRollbackFunction:  constructor(serverless, options) {
    this.serverless = serverless;
    this.options = options || {};
    this.provider = this.serverless.getProvider('aws');

    Object.assign(this, validate);

    this.commands = {
      rollback: {
        commands: {
          function: {
            usage: 'Rollback the function to a specific version',
            lifecycleEvents: [
              'rollback',
            ],
            options: {
              function: {
                usage: 'Name of the function',
                shortcut: 'f',
                required: true,
              },
              version: {
                usage: 'Version of the function',
                shortcut: 'v',
                required: true,
              },
              stage: {
                usage: 'Stage of the function',
                shortcut: 's',
              },
              region: {
                usage: 'Region of the function',
                shortcut: 'r',
              },
            },
          },
        },
      },
    };

    this.hooks = {
      'rollback:function:rollback': () => BbPromise.bind(this)
        .then(this.validate)
        .then(this.getFunctionToBeRestored)
        .then(this.fetchFunctionCode)
        .then(this.restoreFunction),
    };
  }