fixed issue for centos build

include/inc-util/utils.hpp

@@ -7,7 +7,7 @@ namespace IRDB_SDK
 	template <class T>
 	inline string to_hex_string (const T& t)
 	{
-		auto ss=stringstream();
+		stringstream ss();
 		ss << hex << t;
 		return ss.str();
 	}