sub_parser_example.cpp: added stand-alone-purpose to version option

examples/sub_parser_example.cpp

@@ -33,7 +33,7 @@ class cli_parser_t : public clapp::basic_main_parser_t {
 
     // if version is given, print_version_and_exit() is called.
     clapp::bool_option_t version{
-        *this, "version", "Show version info",
+        *this, "version", "Show version info", purpose_t::stand_alone,
         clapp::value::found_func_t{print_version_and_exit}};
 
     clapp::count_option_t verbose{*this,