Migrate to built-in Homebrew-Cask

> Homebrew-Cask will now be kept up to date together with Homebrew

> If you haven’t yet,
> run `brew uninstall --force brew-cask; brew update`
> to switch to the new system.

Homebrew/homebrew-cask@e83c009

> To start using Homebrew-Cask, you just need Homebrew installed.

Homebrew/homebrew-cask@0d290b1

README.md

@@ -106,9 +106,6 @@ For example:
 ```sh
 #!/bin/sh
 
-brew_tap 'caskroom/cask'
-brew_install_or_upgrade 'brew-cask'
-
 brew cask install dropbox
 brew cask install google-chrome
 brew cask install rdio

mac

@@ -132,6 +132,11 @@ else
   fancy_echo "Homebrew already installed. Skipping ..."
 fi
 
+if brew list | grep -Fq brew-cask; then
+  fancy_echo "Uninstalling old Homebrew-Cask ..."
+  brew uninstall --force brew-cask
+fi
+
 fancy_echo "Updating Homebrew formulas ..."
 brew update