README.md: Fix trivial typo

I understand this is quite a trivial fix, but this is my first contribution :-)

Signed-off-by: Gianpaolo Macario <gmacario@gmail.com>

Author: gmacario

README.md

@@ -87,7 +87,7 @@ go test -v ./src/arduino.cc/builder/test/... | bin/go-junit-report > report.xml
 
 ### License and Copyright
 
-`arduino-builder` is licensed under General Public License version 2, as published bythe Free Software Foundation. See [LICENSE.txt](LICENSE.txt).
+`arduino-builder` is licensed under General Public License version 2, as published by the Free Software Foundation. See [LICENSE.txt](LICENSE.txt).
 
 Copyright (C) 2015 Arduino LLC and contributors