make icon white when "Use dark menu bar and Dock" is enabled, or at least make the "White scissors" icon actually white

[jab]

When "Use dark menu bar and Dock" is enabled, it's hard to see the FlyCut icon since it's black on a dark background, even when the "White scissors" icon is selected. Notice how the other menu extras automatically turn white, but FlyCut's doesn't:

Thanks for the great work on FlyCut!

[jab]

Restarted my machine earlier today and just noticed Flycut's icon is now white. Not sure if just restarting Flycut would have done the trick, but I'll leave this open in case it's possible to flip from a black to a white icon when "Use dark menu bar" is toggled on without requiring a restart.