AP_Math: fixed example build

libraries/AP_Math/examples/rotations/rotations.pde

@@ -32,6 +32,7 @@
 #include <AP_Airspeed.h>
 #include <AP_Vehicle.h>
 #include <AP_ADC_AnalogSource.h>
+#include <AP_Rally.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;