百度出来的命令是这样的：brew cask upgrade
然后得出的反馈是这样的：Error: Unknown command: upgrade
解决：
brew cask --help
得到：
Commands:
--version displays the Homebrew-Cask version
audit verifies installability of Casks
cat dump raw source of the given Cask to the standard output
cleanup cleans up cached downloads and tracker symlinks
create creates the given Cask and opens it in an editor
doctor checks for configuration issues
edit edits the given Cask
fetch downloads remote application files to local cache
home opens the homepage of the given Cask
info displays information about the given Cask
install installs the given Cask
list with no args, lists installed Casks; given installed Casks, lists staged files
outdated list the outdated installed Casks
reinstall reinstalls the given Cask
search searches all known Casks
style checks Cask style using RuboCop
uninstall uninstalls the given Cask
zap zaps all files associated with the given Cask
耐心看下去会发现一个这样的命令：reinstall
尝试：brew cask reinstall qq
成功。
学到的是：正确的途径学习获取知识。
