错误：运行firebase云功能时出现“无法找到模块”

const functions = require('firebase-functions');
var nodemailer = require('nodemailer');
// const express=require('express');

var transporter=nodemailer.createTransport('smtps://[email protected]:[email protected]');
exports.sendMail=functions.https.onRequest((req,res)=>{
    var mailOptions={
        to: '[email protected]',
        subject: 'Test Mail',
        html: 'Testing with Node.js'
    }
    transporter.sendMail(mailOptions,function(err,response){
        if(err){
            res.send('Mail not sent');
        }
        else{
            res.send('Mail sent');
        }
    });
});

我从Firebase应用发送邮件。我根据Sending email using Firebase web app提出的问题使用Firebase云功能发送邮件。上面的代码是我的index.js文件。

这是我的package.json文件

{
  "name": "functions",
  "description": "Cloud Functions for Firebase",
  "scripts": {
    "serve": "firebase serve --only functions",
    "shell": "firebase experimental:functions:shell",
    "start": "npm run shell",
    "deploy": "firebase deploy --only functions",
    "logs": "firebase functions:log"
  },
  "dependencies": {
    "firebase-admin": "~5.4.2",
    "firebase-functions": "^0.7.1",
    "sendgrid": "^5.2.3"
  },
  "private": true
}

npm install nodemailer --save

"dependencies": {
  "firebase-admin": "~5.4.2",
  "firebase-functions": "^0.7.1",
  "nodemailer": "^x.x.x",
  "sendgrid": "^5.2.3"
}