title: xcrun: error: invalid active developer path, problem after zsh update for flutter
body: <p>I updated my shell to zsh and when I type flutter --version I get this:</p>
  <pre><code>'''xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools),   
  missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
  Failed to find the latest git commit date: VersionCheckError: Command exited
  with code 1: git -c log.showSignature=false log -n 1 --pretty=format:%ad
  --date=iso
  Standard out: 
  Standard error: xcrun: error: invalid active developer path
  (/Library/Developer/CommandLineTools), missing xcrun at:
  /Library/Developer/CommandLineTools/usr/bin/xcrun
  
  Returning 1970-01-01 01:00:00.000 instead.
  Flutter 0.0.0-unknown • channel unknown • unknown source
  Framework • revision  () • 1970-01-01 01:00:00.000
  Engine • revision b8752bbfff
  Tools • Dart 2.10.2'''
  </code></pre>
  <p>WHAT SHOULD I DO? I'm not an expert in these things XD.</p>
  <p>Kind regards,</p>