USB_HID typo in constant

Hi,

I found a minor issue with the usb_hid.c file, line 656.
It incorrectly maps KEY_3 to 0x40 @. It should be KEY2.
If you look at the rest of the file, KEY3 is mapped to 3, # and @, so when sending an @ to the usbHidKeyCodeFromAsciiChar, it returns Key3, and with a shift modifier, this ends up being #.

Hello. Thanks for catching that! I have fixed it.

–David