自动去官网下载并拖动到/Applications文件夹，并且自动检查更新。
brew cask install macvim brew cask install macdown brew cask install qq brew cask install iterm2查看缓存目录位置
brew cask doctor ==> Homebrew-Cask Cached Downloads ~/Library/Caches/Homebrew/Cask (2 files, 932KB)执行brew cask install macvim 命令后，会出现安装包下载链接，缓冲目录会出现macvim–8.0.135.dmg.incomplete文件。
==> Satisfying dependencies ==> Downloading https://github.com/macvim-dev/macvim/releases/download/snapshot-135/MacVim.dmg若不满于brew的下载速度，并从其他方式（比如浏览器）下载好了安装包MacVim.dmg
将安装包重命名为macvim–8.0.135.dmg替换掉原来的.incomplete 文件重新运行brew cask install macvim ==> Satisfying dependencies ==> Downloading https://github.com/macvim-dev/macvim/releases/download/snapshot-135/MacVim.dmg Already downloaded: /Users/weihuang/Library/Caches/Homebrew/Cask/macvim--8.0.135.dmg ==> Verifying checksum for Cask macvim ==> Installing Cask macvim ==> Moving App 'MacVim.app' to '/Applications/MacVim.app'. ==> Linking Binary 'mvim' to '/usr/local/bin/gview'. ==> Linking Binary 'mvim' to '/usr/local/bin/gvim'. ==> Linking Binary 'mvim' to '/usr/local/bin/gvimdiff'. ==> Linking Binary 'mvim' to '/usr/local/bin/mview'. ==> Linking Binary 'mvim' to '/usr/local/bin/mvim'. ==> Linking Binary 'mvim' to '/usr/local/bin/mvimdiff'. macvim was successfully installed!