fix: result_of_t is deprecated

include/string_utils/traits.h

@@ -14,7 +14,7 @@
 namespace string_utils::detail {
 template <typename, typename = void> struct has_result : std::false_type {};
 template <typename F>
-struct has_result<F, std::void_t<std::result_of_t<F>>> : std::true_type {};
+struct has_result<F, std::void_t<std::invoke_result_t<F>>> : std::true_type {};
 
 template <typename, typename = void> struct is_tuple : std::false_type {};
 template <typename T>