A new version of ChefDK 0.4.0 has been released. I did an upgrade via brew cask

    $ brew update
    ...
    $ brew cask install --force chefdk
    ==> Downloading https://opscode-omnibus-packages.s3.amazonaws.com/mac_os_x/10.8/x86_64/chefdk-0.4.0-1.dmg
    ######################################################################## 100.0%
    ==> Running installer for chefdk; your password may be necessary.
    ==> Package installers may write to any location; options such as --appdir are ignored.
    Password:
    ==> installer: Package name is Chef Development Kit
    ==> installer: Upgrading at base path /
    ==> installer: The upgrade was successful.
    🍺  chefdk staged at '/opt/homebrew-cask/Caskroom/chefdk/0.4.0-1' (6 files, 99M)