MAC 升级版本后brew报错：

brew -v
/usr/local/Homebrew/Library/Homebrew/os/mac/version.rb:33:in `block in from_symbol': unknown or unsupported macOS version: :dunno (MacOSVersionError)
    from /usr/local/Homebrew/Library/Homebrew/os/mac/version.rb:33:in `fetch'
    from /usr/local/Homebrew/Library/Homebrew/os/mac/version.rb:33:in `from_symbol'
    from /usr/local/Homebrew/Library/Homebrew/os/mac.rb:28:in `version'
    from /usr/local/Homebrew/Library/Homebrew/os/mac.rb:60:in `prerelease?'
    from /usr/local/Homebrew/Library/Homebrew/os.rb:43:in `<module:OS>'
    from /usr/local/Homebrew/Library/Homebrew/os.rb:7:in `<top (required)>'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require'
    from /usr/local/Homebrew/Library/Homebrew/global.rb:80:in `<top (required)>'
    from /usr/local/Homebrew/Library/Homebrew/brew.rb:31:in `require_relative'
    from /usr/local/Homebrew/Library/Homebrew/brew.rb:31:in `<main>'

直接更新到最新版本命令：

brew update-reset