I think I may have puzzled this out. The package.json file has under devDependencies:
"grunt-contrib-imagemin": "~0.1.2",
from the logs it looks like this pacakge is dependnt on jpegtran-bin@0.1.7
Looking up this package I found this page:
www.npmjs.com/package/grunt-contrib-imagemin/v/3.1.0
This shows that version 0.1.2 is 7 years old. Changing that dependency to
"grunt-contrib-imagemin": "~2.0.0",
solved the problem. ~3.0.0 didn’t work fyi. too new I guess.
Perhaps someone who is a contributor can let me know if that change is appropriate or a different version would be more compatible.