update includes for dep naming

src/WS2812Serial.h

 #ifndef WS2812Serial_h_
 #define WS2812Serial_h_
 
-#include <Arduino.h>
-#include "DMAChannel.h"
+#include <core/Arduino.h>
+#include <core/DMAChannel.h>
 
 #define WS2812_RGB      0       // The WS2811 datasheet documents this way
 #define WS2812_RBG      1