It seems that you have Xcode 8+ installed! Some plugins might not work on recent versions of Xcode because of library validation. See https://github.com/alcatraz/Alcatraz/issues/475
keyle@xiaonians-MacBook-Pro ~ update_xcode_plugins --unsign Looking for Xcode...
Unsigning Xcode will make it skip library validation allowing it to load plugins. However, an unsigned Xcode presents security risks, and will be untrusted by both Apple and your system. This tool will create a backup and allow you to restore Xcode's signature by running $ update_xcode_plugins --restore
Choose which Xcode you would like to unsign (use arrows): Xcode (10.1) [Signed]: /Applications/Xcode.app Unsign xcodebuild too?: Yes
Unsigning...
* Changing ownership of /Applications/Xcode.app/Contents/MacOS (will be restored after) * Restored ownership of /Applications/Xcode.app/Contents/MacOS
* Changing ownership of /Applications/Xcode.app/Contents/Developer/usr/bin (will be restored after) * Restored ownership of /Applications/Xcode.app/Contents/Developer/usr/bin Finish