nodemailer + art-template template not found

var nodemailer = require("nodemailer")
var template = require("art-template")
var fs = require("fs")
var data = require("./data")

const transporter = nodemailer.createTransport({
  host: 'smtp.163.com',
  port: 465,
  auth: {
    user: '******@163.com',
    pass: '******'
  }
});
var sendmail = function () {
  var html = template(__dirname + '/template/index.html', data)
  var option = {
    from: "*****@163.com",
    to: "******@163.com",
    subject: "test",
    html: html
  }
  transporter.sendMail(option, function (error, response) {
    if (error) {
      console.log("fail:" + error);
    } else {
      console.log("success:" + response.messageId);
    }
  })
}
sendmail()