fix: update py2 warning message (aws#998)

Py2 support is determined by Py2 deprecation date, not TF version.

Author: chuyang-deng

src/sagemaker/tensorflow/estimator.py

@@ -345,7 +345,7 @@ def _validate_args(
 
         if py_version == "py2" and self._only_python_3_supported():
             msg = (
-                "Python 2 containers are only available until TensorFlow version 1.14.0. "
+                "Python 2 containers are only available until January 1st, 2020. "
                 "Please use a Python 3 container."
             )
             raise AttributeError(msg)

tests/unit/test_tf_estimator.py

@@ -959,7 +959,7 @@ def test_py2_version_deprecated(sagemaker_session):
     with pytest.raises(AttributeError) as e:
         _build_tf(sagemaker_session=sagemaker_session, framework_version="1.14.1", py_version="py2")
 
-    msg = "Python 2 containers are only available until TensorFlow version 1.14.0. Please use a Python 3 container."
+    msg = "Python 2 containers are only available until January 1st, 2020. Please use a Python 3 container."
     assert msg in str(e.value)