Corrected a typo in ArduinoAddons/Arduino_1.5.x/(...)/avr/boards.txt about Sanguino

ArduinoAddons/Arduino_1.5.x/hardware/marlin/avr/boards.txt

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 sanguino.name=Sanguino
 
-sanguino.upload.tool=ardunio:avrdude
+sanguino.upload.tool=arduino:avrdude
 sanguino.upload.protocol=stk500
 sanguino.upload.maximum_size=131072
 sanguino.upload.speed=57600