git: missing xcrun
把Mac升级到了macOS High Sierra，发现终端下git用不了了：
xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
直接重新安装xcode解决：
xcode-select –install
把Mac升级到了macOS High Sierra，发现终端下git用不了了：
xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
直接重新安装xcode解决：
xcode-select –install