message: modify example to wotk TF 2.0
diff: @@ -72,13 +72,10 @@ except NameError:
  "only a concern in graph mode. Below is an example "
  "of how to ensure tf.print executes in graph mode:\n"
  """```python
  - sess = tf.Session()
  - with sess.as_default():
  tensor = tf.range(10)
  print_op = tf.print(tensor)
  with tf.control_dependencies([print_op]):
  out = tf.add(tensor, tensor)
  - sess.run(out)
  ```
  Additionally, to use tf.print in python 2.7, users must make sure to import
  the following:
  @@ -159,7 +156,6 @@ def print_v2(*inputs, **kwargs):
  Example:
  Single-input usage:
  ```python
  - tf.enable_eager_execution()
  tensor = tf.range(10)
  tf.print(tensor, output_stream=sys.stderr)
  ```
  @@ -167,7 +163,6 @@ def print_v2(*inputs, **kwargs):
  Multi-input usage:
  ```python
  - tf.enable_eager_execution()
  tensor = tf.range(10)
  tf.print("tensors:", tensor, {2: tensor * 2}, output_stream=sys.stdout)
  ```
  @@ -176,9 +171,8 @@ def print_v2(*inputs, **kwargs):
  Usage in a defun:
  ```python
  - tf.enable_eager_execution()
  -
  - @tf.contrib.eager.defun
  + from tensorflow.python.eager import function
  + @function.defun
  def f():
  tensor = tf.range(10)
  tf.print(tensor, output_stream=sys.stderr)
  @@ -190,14 +184,11 @@ def print_v2(*inputs, **kwargs):
  Usage when constructing graphs:
  ```python
  - sess = tf.Session()
  - with sess.as_default():
  tensor = tf.range(10)
  print_op = tf.print("tensors:", tensor, {2: tensor * 2},
  output_stream=sys.stdout)
  with tf.control_dependencies([print_op]):
  tripled_tensor = tensor * 3
  - sess.run(tripled_tensor)
  ```
  (This prints "tensors: [0 1 2 ... 7 8 9] {2: [0 2 4 ... 14 16 18]}" to
  sys.stdout)
  