How to add uuid as default value using migrations

Issue type:

[x] question [ ] bug report [ ] feature request [ ] documentation issue

Database system/driver:

[ ] cordova [ ] mongodb [ ] mssql [ ] mysql / mariadb [ ] oracle [x] postgres [ ] sqlite [ ] sqljs [ ] react-native [ ] expo

TypeORM version:

[x] latest [ ] @next [ ] 0.x.x (or put your version here)

How could I add uuid_generate_v4() as a default value using typeorm migrations For example,

import { MigrationInterface, QueryRunner, Table } from 'typeorm'
import uuid = require('uuid')

export class InitUserTable1551883596067 implements MigrationInterface {

  public async up(queryRunner: QueryRunner): Promise<any> {
    await queryRunner.createTable(new Table({
      name: 'users',
      columns: [
        {
          name: 'id',
          type: 'uuid',
          isPrimary: true,
          isUnique: true,
          default: '??'
        }
      ]
    }), true)
  }

  public async down(queryRunner: QueryRunner): Promise<any> {
    await queryRunner.dropTable('users', true)
  }

}

If I used sql I would do it this way

CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
COMMIT;

CREATE TABLE users
(
    id         uuid DEFAULT uuid_generate_v4() PRIMARY KEY
);