Following this guideline, `app.js` isn't created

[Exegetech]

I am following this guideline https://github.com/brunch/brunch-guide/blob/master/content/en/chapter04-starting-from-scratch.md

and get to this point where brunch build suppose to create this file structure

public/
├── app.css
├── app.css.map
├── app.js
├── app.js.map
└── index.html

However, only app.css, app.css.map, and index.html got created