It appears that you installed brunch from the git master branch when you generated this error. I was unable to reproduce it using v1.7.10. On master (where I was able to reproduce it), it's just been fixed with https://github.com/brunch/brunch/commit/68dd9c9b6284c05a4eb01050dba56f80f978e35a. So if you reinstall brunch now, either the latest release (1.7.10) or the edge version from git master, the problem you've reported should go away.
Additionally, you might want to reconsider making brunch a dependency of your skeleton in the package.json. Unless there's a specific reason otherwise, it's better to let it just be installed globally. If you want to clarify to users that your skeleton should only be used with brunch versions >=1.7, you can say so in your readme.