Update brew cask

Signed-off-by: Stephen Celis <stephen@stephencelis.com>

Makefile

@@ -71,9 +71,9 @@ homebrew := $(homebrew_root)/bin/brew
 $(homebrew):
 	ruby -e "$$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
 
-brew_cask := $(cellar)/brew-cask
+brew_cask := $(taps)/caskroom/homebrew-cask
 $(brew_cask): | $(homebrew)
-	brew install Caskroom/cask/brew-cask
+	brew tap Caskroom/cask
 
 $(prefixed_formulae): | $(homebrew)
 	brew install $(notdir $@)