Dashed modifiers don't work when acting on numbers (e.g. C-0)

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Trying to set a key to C-0, or using it in a macro, doesn't work. Digging further, the function mugur--qmk-dashed-modifier returns nil when acting on numbers.

(mugur--qmk-dashed-modifier 'C-0)    ;Returns nil

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I believe I have fixed this in #23. Normal numbers and modified numbers both seem to work fine now.