AP_Match: fix example sketch

libraries/AP_Math/examples/polygon/polygon.pde

@@ -11,6 +11,7 @@
 #include <AP_HAL.h>
 #include <AP_HAL_AVR.h>
 #include <AP_HAL_Linux.h>
+#include <AP_Vehicle_Type.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;