It seems that there is a bug in the publish command that occurs if the app-folder is not a Git repository. We will deploy a fix for it. Until then the easiest solution is to actually make it a git repository, by installing Git on your computer and typing the following commands in your cmd in the app-folder:
git init
git config user.email "youremail.example.com"
git add -A && git commit -m "Commit all files for the first time"
Publishing should work after that. Let me know if you have any trouble.