Fix link

examples/hello-world/hello-tf/README.md

@@ -4,7 +4,7 @@ Example of using [NVIDIA FLARE](https://nvflare.readthedocs.io/en/main/index.htm
 using federated averaging ([FedAvg](https://arxiv.org/abs/1602.05629))
 and [TensorFlow](https://tensorflow.org/) as the deep learning training framework.
 
-> **_NOTE:_** This example uses the [MNIST](http://yann.lecun.com/exdb/mnist/) handwritten digits dataset and will load its data within the trainer code.
+> **_NOTE:_** This example uses the [MNIST](https://www.tensorflow.org/datasets/catalog/mnist) handwritten digits dataset and will load its data within the trainer code.
 
 See the [Hello TensorFlow](https://nvflare.readthedocs.io/en/main/examples/hello_tf_job_api.html#hello-tf-job-api) example documentation page for details on this
 example.