Update boards.h

Marlin/boards.h

@@ -78,6 +78,7 @@
 #define BOARD_MEGATRONICS_2     701  // Megatronics v2.0
 #define BOARD_MINITRONICS       702  // Minitronics v1.0/1.1
 #define BOARD_MEGATRONICS_3     703  // Megatronics v3.0
+#define BOARD_MEGATRONICS_31    704  // Megatronics v3.1
 #define BOARD_OMCA_A            90   // Alpha OMCA board
 #define BOARD_OMCA              91   // Final OMCA board
 #define BOARD_RAMBO             301  // Rambo