AP_GPS: add includes for success build example sketch

include AP_Scheduler.h for achieve build GPS_UBLOX_passthrough example

libraries/AP_GPS/examples/GPS_UBLOX_passthrough/GPS_UBLOX_passthrough.pde

@@ -35,6 +35,7 @@
 #include <AP_Notify.h>
 #include <AP_NavEKF.h>
 #include <AP_Rally.h>
+#include <AP_Scheduler.h>
 #include <AP_BattMonitor.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;