AP_Motors: fixed example build

libraries/AP_Motors/examples/AP_Motors_Time_test/AP_Motors_Time_test.pde

@@ -31,6 +31,7 @@
 #include <AP_Vehicle.h>
 #include <AP_ADC_AnalogSource.h>
 #include <AP_Mission.h>
+#include <AP_Terrain.h>
 #include <AP_NavEKF.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;

libraries/AP_Motors/examples/AP_Motors_test/AP_Motors_test.pde

@@ -31,6 +31,7 @@
 #include <AP_Vehicle.h>
 #include <AP_ADC_AnalogSource.h>
 #include <AP_Mission.h>
+#include <AP_Terrain.h>
 #include <AP_NavEKF.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;