code: function saveWallet(filename, walletData) {
    return new Promise((resolve, reject) => {
      fs.writeFile(filename, JSON.stringify(walletData, null, 2), function(err) {
        if (err) return reject(console.error(err))
  
        //console.log(`${name}.json written successfully.`)
        return resolve()
      })
    })
  }
docs: Save a wallet to a file.