volo url attribute pointing to broken URL generates confusing error msg

[dmose]

I created an override package.json with a bug in that it pointed to an https URL where there was no server running, rather than
the correct http URL. The error message given makes it looks like the problem happened while contacting github:

volo add crafty
Using github repo "craftyjs/Crafty" for "crafty"...
Error: connect ECONNREFUSED

By the time you read this, I expect to have fixed the override volofile, but it should be easy to reproduce. :-)