switch is-os-dark-mode function to the old implementation
switch is-os-dark-mode function to the old implementation

Use this again:
```
osascript -l JavaScript -e 'Application("System Events").appearancePreferences.darkMode()'
```

instead of:
```
defaults read -g AppleInterfaceStyle
```

because the latter incorrectly reports "Dark" even when the OS is
already in light mode.

chuckeles/dotfiles