Your package is missing nodemon so when running npm start, it fails.
run this command and commit:
npm install -D nodemon

Also, a side note, you might want to separate your dependancies and dev dependancies in your package as well. Besides that, great example of passport with mongojs.

If you want to convert to es6 with using babel:
npm install -D babel-cli babel-preset-es2015

create a new file in your root directory called .babelrc and use this code:
{ "presets": ["es2015"] }

in your package.json, change your start script to : ``"start": "nodemon app.js --exec babel-node"

and if you want to add a build & serve command for running on production:
"build": "babel app.js -d dist", "serve": "node dist/app.js"