macOS Mojaveでのbrew updateエラーを解消する

Mojaveでbrew updateするとエラー

$ brew update
xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun

ググって見たらとりあえずbrew doctorすると良いらしい

$ brew doctor
Please note that these warnings are just used to help the Homebrew maintainers
with debugging if you file an issue. If everything you use Homebrew for is
working fine: please don't worry or file an issue; just ignore this. Thanks!

Warning: The following directories do not exist:
/usr/local/sbin

You should create these directories and change their ownership to your account.
  sudo mkdir -p /usr/local/sbin
  sudo chown -R $(whoami) /usr/local/sbin

Warning: Your Xcode is configured with an invalid path.
You should change it to the correct path:
  sudo xcode-select -switch /Applications/Xcode.app

Warning: Broken symlinks were found. Remove them with `brew prune`:
  /usr/local/bin/docker-credential-osxkeychain.backup
  /usr/local/bin/hyperkit.backup
  /usr/local/bin/notary.backup
  /usr/local/bin/scan
  /usr/local/bin/vpnkit.backup
  /usr/local/share/man/man1/scan.1

なんか色々出てきた

元々のエラーに関連するWarningは真ん中のやつっぽい

Warning: Your Xcode is configured with an invalid path.
You should change it to the correct path:
  sudo xcode-select -switch /Applications/Xcode.app

こことか見ても単にinstallしてしまえば良さそう。LaunchPadからXcodeを実行すると確認ダイアログが出てinstallで終了
再びbrew updateするとエラーが解消済みだった

(2018/11/20 更新)再度brew updateすると同じエラーが再発したのでWarningのコマンドを実行して解消

$ brew update
Already up-to-date.

他のWarningは何だろう。docker関連かな。。。。