Update epd2in13.py

This will allow the screen to be cleared without the color parameter being explicitly included (similar to the 2in7 library)

RaspberryPi_JetsonNano/python/lib/waveshare_epd/epd2in13.py

@@ -201,7 +201,7 @@ class EPD:
                 self.send_data(image[i + j * linewidth])   
         self.TurnOnDisplay()
     
-    def Clear(self, color):
+    def Clear(self, color=0xFF):
         if self.width%8 == 0:
             linewidth = int(self.width/8)
         else: