Ristretto - Update bootloader (#13933)

* updated bootloader for 32u4 mcu

Should be atmel-dfu instead of caterina as the mcu is integrated instead of on a pro-micro/elite-c

keyboards/ristretto/rules.mk

@@ -2,7 +2,7 @@
 MCU = atmega32u4
 
 # Bootloader selection
-BOOTLOADER = caterina
+BOOTLOADER = atmel-dfu
 
 # Build Options
 #   change yes to no to disable