install brew cask

os x install brew cask '/usr/../../brew-cask.rb' does not exist
brew 安装完毕，安装brew cask

brew install caskroom/cask/brew-cask

出现error：

Error: Cask 'brew-cask' is unavailable: '/usr/local/Homebrew/Library/Taps/caskroom/homebrew-cask/Casks/brew-cask.rb' does not exist. 

方法：
使用如下

brew install brew-cask-completion

测试
输入如下：

brew cask search qq

返回结果如下则成功：

==> Exact Match
qq
==> Partial Matches
qqbrowser       qqinput         qqlive          qqmacmgr        qqmusic