Update 404 link (tensorflow#244)

* Update 404 link

Author: GantMan

mnist/README.md

@@ -2,7 +2,7 @@
 
 This example shows you how to train MNIST (using the layers API).
 
-You can check out the tutorial that accompanies this example [here](https://js.tensorflow.org/tutorials/mnist.html).
+You can check out the tutorial that accompanies this example [here](https://www.tensorflow.org/js/tutorials/training/handwritten_digit_cnn).
 
 This model will compute accuracy over 1000 random test set examples every 5
 steps, plotting loss and accuracy as the model is training. Training time can