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

@@ -1,14 +1,14 @@
-SBUS  KEYWORD1
+SBUS	KEYWORD1
 
-begin KEYWORD2
-process KEYWORD2
-getChannel  KEYWORD2
-getNormalizedChannel  KEYWORD2
-getFailsafeStatus KEYWORD2
-getFrameLoss  KEYWORD2
-getGoodFrames KEYWORD2
-getLostFrames KEYWORD2
-getDecoderErrorFrames KEYWORD2
+begin	KEYWORD2
+process	KEYWORD2
+getChannel	KEYWORD2
+getNormalizedChannel	KEYWORD2
+getFailsafeStatus	KEYWORD2
+getFrameLoss	KEYWORD2
+getGoodFrames	KEYWORD2
+getLostFrames	KEYWORD2
+getDecoderErrorFrames	KEYWORD2
 
-SBUS_FAILSAFE_INACTIVE LITERAL1
-SBUS_FAILSAFE_ACTIVE LITERAL1
+SBUS_FAILSAFE_INACTIVE	LITERAL1
+SBUS_FAILSAFE_ACTIVE	LITERAL1