async createUser (username, password, groupId, comment = '', from = '') {
    if (!await this.checkUsername(username)) return -1

    const result = await db('users').insert({
      username,
      password: bcrypt.hashSync(password, bcrypt.genSaltSync()),
      token: randomString.generate(32),
      permission_group: groupId,
      from,
      comment,
      createTime: (new Date()).getTime(),
      lastSeen: (new Date()).getTime()
    }).select('id')

    return result[0]
  }
Create user

@param {String} username username
@param {String} password user password
@param {Int} groupId permission group id
@param {String=} comment comment
@param {String=} from from

@returns {Int} username id