[mdm publish github] does not work for existing repo

[pingpongboss]

I noticed that https://github.com/material-motion/material-motion-family-tween-android was missing gh-pages and stable and thought I'd run mdm publish github android material-motion material-motion-family-tween-android to generate those branches. However, it failed with

$ mdm publish github android material-motion material-motion-family-tween-android
About to create a new GitHub repository.
Please confirm the details below:

    URL: https://github.com/material-motion/material-motion-family-tween-android
    Command: mdm gh repo -u material-motion --new material-motion-family-tween-android

Press enter to continue...
Creating a new repo on material-motion/material-motion-family-tween-android
[ { resource: 'Repository',
    code: 'custom',
    field: 'name',
    message: 'name already exists on this account' } ]