Fix MKR Vidor 4000 Serial.dtr

This value is incorrect and prevents GPIO0 from being pulled at the right time, so esptool could not detect the board at all.
Now, it works perfectly with the added --no-stub parameter.
See this forum post for further discussion: https://forum.arduino.cc/index.php?topic=596970.0

examples/Tools/SerialNINAPassthrough/SerialNINAPassthrough.ino

@@ -74,7 +74,7 @@ void loop() {
 
   if (dtr != Serial.dtr()) {
 #ifdef ARDUINO_SAMD_MKRVIDOR4000
-    FPGA.digitalWrite(FPGA_NINA_GPIO0, (Serial.dtr() == 1) ? HIGH : LOW);
+    FPGA.digitalWrite(FPGA_NINA_GPIO0, (Serial.dtr() == 0) ? HIGH : LOW);
 #else
     digitalWrite(NINA_GPIO0, (Serial.dtr() == 0) ? HIGH : LOW);
 #endif