fix replace to_string by stringstream

src/ulib/status.cpp

@@ -66,9 +66,11 @@ StatusCodeToString(StatusCode code)
         return "UNAVAILABLE";
     case StatusCode::kDataLoss:
         return "DATA_LOSS";
-    default:
-        return "UNEXPECTED_STATUS_CODE="
-            + std::to_string(static_cast<int>(code));
+    default: {
+        std::stringstream ss;
+        ss << "UNEXPECTED_STATUS_CODE=" << static_cast<int>(code);
+        return ss.str();
+    }
     }
 }