Update bcu.rb to require "cask", not "cask/all"
Update bcu.rb to require "cask", not "cask/all"

Homebrew/brew#8262 moved `cask/all` to `cask`, which breaks this command. This change fixes it.
buo/brew-cask-upgrade,buo/homebrew-cask-upgrade,buo/homebrew-cask-upgrade,buo/brew-cask-upgrade