toString for bool value (true/false)

src/artis/kernel/Value.hpp

@@ -113,7 +113,7 @@ public:
                         dynamic_cast < data < T, bool >* >(ptr_);
 
                     if (q_bool) {
-                        return std::to_string(o->*(q_bool->value_));
+                        return o->*(q_bool->value_) ? "true": "false";
                     } else {
                         return "NA";
                     }