Update CONTRIBUTING.md tensorflow/tensorflow

CONTRIBUTING.md

@@ -72,7 +72,7 @@ TensorFlow coding style.
     [tensorflow/core](https://github.com/tensorflow/tensorflow/tree/master/tensorflow/core)
     and
     [tensorflow/python](https://github.com/tensorflow/tensorflow/tree/master/tensorflow/python).
-    TensorFlow has reached version 1 and hence cannot make
+    TensorFlow has reached version 2 and hence cannot make
     non-backward-compatible API changes without a major release. Reviewers of
     your pull request will comment on any API compatibility issues.
 *   When you contribute a new feature to TensorFlow, the maintenance burden is