correct VGG19 model link

Author: zsdonghao

README.md

@@ -25,7 +25,7 @@ TensorFlow Implementation of ["Photo-Realistic Single Image Super-Resolution Usi
 ### Prepare Data and Pre-trained VGG
 - In this experiment, we used images from [DIV2K - bicubic downscaling x4 competition](http://www.vision.ee.ethz.ch/ntire17/), besides [Yahoo MirFlickr25k](http://press.liacs.nl/mirflickr/mirdownload.html) is also a good choice. Alternatively, you can use your own data by setting your image folder in `config.py`.
 
-- Download VGG model as [tutorial_vgg16.py](https://github.com/zsdonghao/tensorlayer/blob/master/example/tutorial_vgg16.py) show.
+- Download VGG model as [tutorial_vgg19.py](https://github.com/zsdonghao/tensorlayer/blob/master/example/tutorial_vgg19.py) show.