How to use npm modules on grunt?

Earlier when I was using node.js without grunt I had to simply write the following code to include an external module.

var express  = require('express');

After I switched to grunt I am trying to use the following module qr-image.

I am stuck with the use of this module as whenever I use the following command my code breaks.

[ This is as per an official example. ]

var qr = require('../');

To Install this module in my node_modules directory I changed the package.json by adding the following dependency in

"devDependencies": {
    .
    .
    .

    "qr-image": "^2.0.0"
}, 

And then ran npm install command at the root directory level of my app.

Thus, Stuck with the implementation of this node.js qr-image module on grunt. Any help will be appreciated.