Update DHTtester.ino

examples/DHTtester/DHTtester.ino

@@ -22,6 +22,15 @@
 
 DHT dht(DHTPIN, DHTTYPE);
 
+#if defined(ARDUINO_ARCH_AVR)
+#define debug  Serial
+
+#elif defined(ARDUINO_ARCH_SAMD) ||  defined(ARDUINO_ARCH_SAM)
+#define debug  SerialUSB
+#else
+#define debug  Serial
+#endif
+
 void setup() 
 {