Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -4,8 +4,8 @@ We'd love to hear your feedback. Please open new issues describing any bugs,
 feature requests or suggestions that you have.
 
 We will also consider high quality pull requests. These should normally merge
-into the [dev][] branch, not master. To contribute in this way you must first
-submit a Contributor License Agreement, as described below.
+into the [dev][] branch rather than master. To contribute in this way you must
+first submit a Contributor License Agreement, as described below.
 
 [dev]: https://github.com/google/ExoPlayer/tree/dev