message: fix doc bug for per_image_standardization (unit norm vs. variance)
diff: @@ -1176,7 +1176,7 @@ def resize_image_with_pad(image,
  @tf_export('image.per_image_standardization')
  def per_image_standardization(image):
  - """Linearly scales `image` to have zero mean and unit norm.
  + """Linearly scales `image` to have zero mean and unit variance.
  This op computes `(x - mean) / adjusted_stddev`, where `mean` is the average
  of all values in image, and
  