让Mac Dock栏的时钟动起来

显示秒针（可能增加耗电）

defaults write com.apple.dock.extra com.apple.clock.docktile.showSecondHand -bool YES
killall Dock

关闭显示

defaults write com.apple.dock.extra com.apple.clock.docktile.showSecondHand -bool NO
killall Dock