AC_WPNav: fixed example build

libraries/AC_WPNav/examples/AC_WPNav_test/AC_WPNav_test.pde

@@ -37,6 +37,7 @@
 #include <DataFlash.h>
 #include <GCS_MAVLink.h>
 #include <AP_Mission.h>
+#include <StorageManager.h>
 #include <AP_Terrain.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;