InertialSensor: fix example sketch

libraries/AP_InertialSensor/examples/INS_generic/INS_generic.pde

@@ -39,6 +39,7 @@
 #include <AP_Rally.h>
 #include <AP_Scheduler.h>
 #include <AP_BattMonitor.h>
+#include <AP_RangeFinder.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;