message: fix: import error
diff: @@ -441,7 +441,8 @@ module. Consider the simple case where we want to train the VGG network:
  ```python
  import tensorflow as tf
  -vgg = tf.contrib.slim.nets.vgg
  +import tensorflow.contrib.slim.nets as nets
  +vgg = nets.vgg
  # Load the images and labels.
  images, labels = ...
  @@ -559,9 +560,10 @@ examine the following sample of training the VGG network:
  ```python
  import tensorflow as tf
  +import tensorflow.contrib.slim.nets as nets
  slim = tf.contrib.slim
  -vgg = tf.contrib.slim.nets.vgg
  +vgg = nets.vgg
  ...
  @@ -809,9 +811,10 @@ Putting it all together:
  ```python
  import tensorflow as tf
  +import tensorflow.contrib.slim.nets as nets
  slim = tf.contrib.slim
  -vgg = tf.contrib.slim.nets.vgg
  +vgg = nets.vgg
  # Load the data
  