#480 Added a redirect from serial.port.file to serial.port

This should fix 1.6.8 from SAM package.
I'm not sure what the OP is using as this contains another definition

Author: jantje

it.baeyens.arduino.core/config/pre_processing_platform_default.txt

@@ -15,4 +15,7 @@ esp8266.network.upload.tool=esp8266OTA
 TOOLS.ESPTOOL.NETWORK.PASSWORD={NETWORK.AUTH}
 
 #for yun shield to work
-TOOLS.AVRDUDE_REMOTE.UPLOAD.VERBOSE=-v
+TOOLS.AVRDUDE_REMOTE.UPLOAD.VERBOSE=-v
+
+#for due
+serial.port.file={serial.port}