Use correct field separator in keywords.txt

The Arduino IDE requires the use of a single true tab separator between the keyword name and identifier. When spaces are used rather than a true tab the keyword is not highlighted.

Reference:
https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5:-Library-specification#keywords

keywords.txt

@@ -23,4 +23,4 @@ zeroCalibrate	KEYWORD2
 #######################################
 # Constants (LITERAL1)
 #######################################
-ITG3200 LITERAL1
+ITG3200	LITERAL1