If you have a look at the package.json you’ll find.
"main": "Gruntfile.js",
https://docs.npmjs.com/files/package.json#main
The main field is a module ID that is the primary entry point to your program. That is, if your package is named foo, and a user installs it, and then does require(“foo”), then your main module’s exports object will be returned.
This should be a module ID relative to the root of your package folder.
For most modules, it makes the most sense to have a main script and often not much else.
Gruntfile.js is a taskrunner configuration file. As far as I can tell that package is not suitable for bundling by Brunch or any other bundler (FYI: Phoenix is moving to Webpack 4).
This problem happens frequently with older JavaScript libraries that are barely being maintained (another example).
