"From PyTorch to PyTorch Lightning" outdated
🐛 Bug
When using the example code from the documentation "From PyTorch to PyTorch Lightning". In the newest version 0.7.1 you get the error AttributeError: 'LightningMNISTClassifier' object has no attribute 'mnist_val'.
To Reproduce
Steps to reproduce the behavior:

Install version 0.7.1 from pytorch-ignite
Copy Code at the bottom of the page from the doc  "From PyTorch to PyTorch Lightning"
Run it
See error

Stacktrace
  File "D:\Programme\Anaconda3\envs\pytorch\lib\site-packages\pytorch_lightning\trainer\trainer.py", line 630, in fit
    self.run_pretrain_routine(model)
  File "D:\Programme\Anaconda3\envs\pytorch\lib\site-packages\pytorch_lightning\trainer\trainer.py", line 796, in run_pretrain_routine
    self.reset_val_dataloader(ref_model)
  File "D:\Programme\Anaconda3\envs\pytorch\lib\site-packages\pytorch_lightning\trainer\data_loading.py", line 154, in reset_val_dataloader
    self.val_dataloaders = self.request_data_loader(model.val_dataloader)
  File "D:\Programme\Anaconda3\envs\pytorch\lib\site-packages\pytorch_lightning\trainer\data_loading.py", line 220, in request_data_loader
    data_loader = data_loader_fx()
  File "C:/Users/schup/PycharmProjects/Workspace/pytorch_test/GAN/cnn_from_towardsdatascience.py", line 85, in val_dataloader
    mnist_val = DataLoader(self.mnist_val, batch_size=64)
  File "D:\Programme\Anaconda3\envs\pytorch\lib\site-packages\torch\nn\modules\module.py", line 576, in __getattr__
    type(self).__name__, name))
AttributeError: 'LightningMNISTClassifier' object has no attribute 'mnist_val'

Code sample
Code
Article
Expected behavior
The example should provide a working MNIST classifier.
Environment
PyTorch version: 1.4.0
Is debug build: No
CUDA used to build PyTorch: 10.1
OS: Microsoft Windows 10 Pro
GCC version: Could not collect
CMake version: Could not collect
Python version: 3.7
Is CUDA available: Yes
CUDA runtime version: 10.2.89
GPU models and configuration: GPU 0: GeForce GTX 1050 Ti
Nvidia driver version: 442.19
cuDNN version: Could not collect
Versions of relevant libraries:
[pip3] numpy==1.16.1
[conda] blas                      1.0                         mkl
[conda] mkl                       2020.0                      166
[conda] mkl-service               2.3.0            py37hb782905_0
[conda] mkl_fft                   1.0.15           py37h14836fe_0
[conda] mkl_random                1.1.0            py37h675688f_0
[conda] pytorch                   1.4.0           py3.7_cuda101_cudnn7_0    pytorch
[conda] pytorch-ignite            0.4.0.dev20200229          pypi_0    pypi
[conda] pytorch-lightning         0.7.1                    pypi_0    pypi
[conda] torchvision               0.4.1                    pypi_0    pypi
[conda] torchviz                  0.0.1                    pypi_0    pypi