Update ChangeUID.ino

Updated code to account for serial behavior change in ATMEGA32U4

examples/ChangeUID/ChangeUID.ino

@@ -51,7 +51,8 @@ MFRC522::MIFARE_Key key;
 
 void setup() {
         Serial.begin(9600);        // Initialize serial communications with the PC
-        SPI.begin();                // Init SPI bus
+        while (!Serial);           // Do nothing if no serial port is opened (added for Arduinos based on ATMEGA32U4)
+        SPI.begin();               // Init SPI bus
         mfrc522.PCD_Init();        // Init MFRC522 card
         Serial.println("Warning: this example overwrites the UID of your UID changeable card, use with care!");