D3: project Choropleth Map "No geoJson file"

This project wants me to create US map using this file

https://raw.githubusercontent.com/no-stack-dub-sack/testable-projects-fcc/master/src/data/choropleth_map/counties.json

The problem is it is not a geoJson file, So how am I suppose to create a map without a geoJson file?