Update board.py

Changed LED pin name from "BOARD_LED" to "LED".

Author: NathanaelChao

XRPLib/board.py

@@ -17,7 +17,7 @@ def get_default_board(cls):
         return cls._DEFAULT_BOARD_INSTANCE
 
     def __init__(self, vin_pin="BOARD_VIN_MEASURE", button_pin="BOARD_USER_BUTTON", 
-                 rgb_led_pin = "BOARD_NEOPIXEL", led_pin = "BOARD_LED"):
+                 rgb_led_pin = "BOARD_NEOPIXEL", led_pin = "LED"):
         """
         Implements for extra features on the XRP v2 board. Handles the on/off switch, button, and LED.