Magick::QuantumDepth removed

[johlym]

Should be replaced with MAGICKCORE_QUANTUM_DEPTH as per rmagick/rmagick#167

[ben-j69]

👍

[nathanpc]

I completely forgot about this library, sorry for that. I've updated it anyway. Thanks for reporting the change!

[charlesangelolai]

Running into this same issue with the uninitialized constant Magick::QuantumDephth