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

Author: per1234

keywords.txt

@@ -1,3 +1,3 @@
-FileCache   KEYWORD1
-put         KEYWORD2
-get         KEYWORD2
+FileCache	KEYWORD1
+put	KEYWORD2
+get	KEYWORD2