AP_GPS: fixed examples build

libraries/AP_GPS/examples/GPS_406_test/GPS_406_test.pde

@@ -13,6 +13,7 @@
 #include <AP_HAL.h>
 #include <AP_HAL_AVR.h>
 #include <AP_GPS.h>
+#include <AP_Notify.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;
 

libraries/AP_GPS/examples/GPS_MTK_test/GPS_MTK_test.pde

@@ -16,6 +16,7 @@
 #include <AP_HAL_Empty.h>
 #include <AP_GPS.h>
 #include <AP_Math.h>
+#include <AP_Notify.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;
 

libraries/AP_GPS/examples/GPS_NMEA_test/GPS_NMEA_test.pde

@@ -13,6 +13,7 @@
 #include <AP_HAL_AVR.h>
 #include <AP_HAL_AVR_SITL.h>
 #include <AP_HAL_Empty.h>
+#include <AP_Notify.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;
 

libraries/AP_GPS/examples/GPS_UBLOX_test/GPS_UBLOX_test.pde

@@ -16,6 +16,7 @@
 #include <AP_HAL_PX4.h>
 #include <AP_GPS.h>
 #include <AP_Math.h>
+#include <AP_Notify.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;