message: Fix "Define the model" link.
  The link syntax was inverted, that is, round brackets were coming before square brackets, but Markdown doesn't like it.
diff: @@ -161,7 +161,7 @@ classifier = tf.estimator.Estimator(
  To implement a typical model function, you must do the following:
  -* (Define the model)[#define_the_model].
  +* [Define the model](#define_the_model).
  * Specify additional calculations for each of
  the [three different modes](#modes):
  * [Predict](#predict)
  