Remove unnecessary git command from build instructions (#5572)

tylerbwong · akarnokd · commit ad8cd0cf7b1e · 2017-08-28T09:55:53.000+02:00
diff --git a/README.md b/README.md
@@ -250,7 +250,6 @@ To build:
 ```
 $ git clone git@github.com:ReactiveX/RxJava.git
 $ cd RxJava/
-$ git checkout -b 2.x
 $ ./gradlew build
 ```
 
