Running through your CR tutorial and running the command git heatmap --width 25 --filter 'grep src | grep "\.js"', as well as just git heatmap by itself. Problem is, when I run these commands, I get blank output:

running git-heatmap -help and bars by themselves show the help pages, so I can confirm that both are installed properly.

I am using zsh 5.8 (Darwin), along with node 13.5.0.