Mission: fix example sketch

libraries/AP_Mission/examples/AP_Mission_test/AP_Mission_test.pde

@@ -36,6 +36,7 @@
 #include <AP_Buffer.h>          // ArduPilot general purpose FIFO buffer
 #include <GCS_MAVLink.h>
 #include <AP_BattMonitor.h>
+#include <AP_RangeFinder.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;