message: model_dir keyword argument repeated
  In the code repeats the model_dir keyword argument, causing a syntax error if you try to run it (`SyntaxError: keyword argument repeated`).  This remove the second occurrence of the model_dir param.
diff: @@ -426,8 +426,7 @@ m = tf.estimator.LinearClassifier(
  optimizer=tf.train.FtrlOptimizer(
  learning_rate=0.1,
  l1_regularization_strength=1.0,
  - l2_regularization_strength=1.0),
  - model_dir=model_dir)
  + l2_regularization_strength=1.0))
  ```
  One important difference between L1 and L2 regularization is that L1
  