fixed issue for centos build

include/inc-util/utils.hpp

+#include <sstream>
 
 namespace IRDB_SDK
 {
@@ -7,7 +8,7 @@ namespace IRDB_SDK
 	template <class T>
 	inline string to_hex_string (const T& t)
 	{
-		stringstream ss();
+		stringstream ss;
 		ss << hex << t;
 		return ss.str();
 	}
@@ -16,7 +17,7 @@ namespace IRDB_SDK
 
 	template<class T> inline T strtoint(const string& s)
 	{
-		auto str=stringstream(s);
+		stringstream str(s);
 		auto off=T();
 
 		str >> off;