Add compatability for Cherry 3u Spacebars

[epicfacethe3rd]

Sources from dimensioning taken from deskauthority. Will be buying a set of stab wires soon to see if this indeed matches what they claim there https://deskthority.net/wiki/Space_bar_dimensions#3_units_.2857mm_wide.2C_3_mounts.2C_19.05mm_apart.29

[epicfacethe3rd]

hope this helps!