Nodemailer throws error Invalid login: 534-5.7.14

You might need to allow access to your Gmail account.

https://accounts.google.com/b/0/DisplayUnlockCaptcha

Edit (after your comment)

// create reusable transporter object using the default SMTP transport

transporter = nodemailer.createTransport({
    host: 'smtp.gmail.com',
    port: 465,
    secure: true, 
    auth: {
        user: 'yourEmail', 
        pass: 'yourPassword' 
    }
});

your ‘nodemailer.createTransport’ should look something similar.