Error deploy firebase function

I have an Angular project and doing the deploy of my function gives me this error:

  

! functions [sendEmailConfirmation]: Deployment error.   Function load error: Code in file index.js can not be loaded.   Did you list all required modules in the package.json dependencies?   Detailed stack trace: Error: Can not find module 'nodemailer'

I made npm install nodemailer and I have it in my dependencies of the package.json:

"nodemailer": "^4.6.4",
"firebase": "^4.12.0",
"firebase-admin": "^5.12.0",

My index.js:

const nodemailer = require('nodemailer');