src/clapp/sub_parser.cpp: introduced more const

src/clapp/sub_parser.cpp

@@ -22,7 +22,7 @@ clapp::parser::basic_sub_parser_t::sub_parse(types::arg_iterator_t begin,
                                              types::arg_iterator_t end) {
     active = true;
     for (types::arg_iterator_t it = begin; it != end;) {
-        std::string_view option{*it};
+        const std::string_view option{*it};
         parse_result_t parse_result{parse(option, it, end)};
         if (parse_result.exit) {
             return parse_result;