Hello @Bruce_Robinson 
First of all, I have not heard about/used grunt/gulp server and don’t have any experiences with it, and am not a Mac user either. But the SSL/HTTPS error issue (on Mac) you reported sounds familiar to me.
Maybe you may want to check the other thread and this thread , and see if that solution will help to solve that SSL/HTTPS error issue on your end?
Last week or so, my colleague also added the step-by-step on how to do that in the other thread here.
Please let us know with the results.
Cheers,
Agus