I managed to get the upgrade working, was a little bit of a struggle.
General Steps
1. Install new Vagrant DMG (on mac)
2. Uninstall Vagrant Gem (from system, rvm, bundler whatever)
3. Install Berkshelf Vagrant Plugin (`vagrant plugin install berkshelf-vagrant`)
4. Upgrade Berkshelf Gem to 1.3.*
5. Rerun Berks install
6. Remove any 'require Berkshelf' sections from my Vagrantfile
7. Remove references to 'config.berkshelf.berksfile_path' from Vagrantfile
Notes:
`vagrant up` seems to not do a `vagrant provision` automatically, so now I have to chain the commands.
The `.vagrant` file is now actually a folder, so make sure to use rm -rf to clean up afterwards.
Granted my Vagrantfiles are very simple, so there may be more conversion needed.