chmod (remotePath, mode) {
    return new Promise((resolve, reject) => {
      const { sftp } = this
      sftp.chmod(remotePath, mode, (err) => {
        if (err) reject(err)
        else resolve(1)
      })
    })
  }
chmod

@param {String} remotePath
https://github.com/mscdex/ssh2/blob/master/SFTP.md
@return {Promise}