今天更新 Homebrew 之後，啟動 vim 時顯示錯誤：
dyld: Library not loaded: /usr/local/opt/ruby/lib/libruby.2.4.3.dylib
Referenced from: /usr/local/bin/vim
Reason: image not found
[1] 52248 abort vim
找到類似問題，原因是 vim 依賴舊版的 ruby，所以更新後無法啟動，解決方法是重裝 ruby 和 vim：
brew reinstall ruby vim
但我重裝之後仍然無法使用，顯示如下錯誤訊息：
Error: The `brew link` step did not complete successfully
The formula built, but is not symlinked into /usr/local
Could not symlink bin/rake
Target /usr/local/bin/rake
already exists. You may want to remove it:
rm '/usr/local/bin/rake'
To force the link and overwrite all conflicting files:
brew link --overwrite ruby
To list all files that would be deleted:
brew link --overwrite --dry-run ruby
照著提示使用 brew link --overwrite ruby，再重新更新 vim：
brew upgrade vim
如此一來，ruby 成功更新到最新版，且 vim 的依賴也是新版的 ruby，就能正常啟動了！
另外，如果不想更新 vim，其實也可以直接讓 ruby 降版（參考這篇）：
# 確認目前有哪些版本
brew info ruby
# 顯示訊息如下
ruby: stable 2.5.0 (bottled), HEAD
Powerful, clean, object-oriented scripting language
https://www.ruby-lang.org/
/usr/local/Cellar/ruby/2.4.3_1 (3,043 files, 16.3MB)
Poured from bottle on 2017-12-22 at 00:00:26
/usr/local/Cellar/ruby/2.5.0 (3,323 files, 18.4MB)
Poured from bottle on 2018-01-25 at 10:21:10
# 切換版本
brew switch ruby 2.4.3_1