Move code of conduct to .github org repository
Move code of conduct to .github org repository

This is now available globally for the project here: https://github.com/dokku/.github/blob/master/CODE_OF_CONDUCT.md

Closes #3813
claytonbrown/dokku,dokku/dokku,progrium/dokku,claytonbrown/dokku,dokku/dokku,dokku/dokku,claytonbrown/dokku,dokku/dokku,progrium/dokku,dokku/dokku,claytonbrown/dokku,progrium/dokku,progrium/dokku,progrium/dokku,claytonbrown/dokku,progrium/dokku,progrium/dokku,dokku/dokku,claytonbrown/dokku,dokku/dokku,progrium/dokku,claytonbrown/dokku,claytonbrown/dokku,dokku/dokku