Fix MNIST 404 with torchvision>=0.9.1

[akihironitta]

What does this PR do?

Fixes #673.

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[codecov]

Codecov Report

Merging #674 (501746d) into master (9990749) will increase coverage by 46.68%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           master     #674       +/-   ##
===========================================
+ Coverage   25.56%   72.24%   +46.68%     
===========================================
  Files         118      118               
  Lines        7111     7145       +34     
===========================================
+ Hits         1818     5162     +3344     
+ Misses       5293     1983     -3310     

Flag	Coverage Δ
cpu	72.24% <100.00%> (+46.68%)	⬆️
pytest	72.24% <100.00%> (+46.68%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pl_bolts/utils/__init__.py	92.59% <100.00%> (ø)
pl_bolts/losses/self_supervised_learning.py	71.33% <0.00%> (+0.18%)	⬆️
pl_bolts/models/self_supervised/cpc/cpc_module.py	20.58% <0.00%> (+0.58%)	⬆️
pl_bolts/models/vision/image_gpt/igpt_module.py	20.65% <0.00%> (+0.87%)	⬆️
pl_bolts/datasets/imagenet_dataset.py	20.00% <0.00%> (+1.50%)	⬆️
pl_bolts/datasets/kitti_dataset.py	34.61% <0.00%> (+1.92%)	⬆️
pl_bolts/callbacks/vision/confused_logit.py	26.02% <0.00%> (+4.10%)	⬆️
pl_bolts/callbacks/printing.py	71.18% <0.00%> (+6.77%)	⬆️
pl_bolts/models/rl/common/cli.py	11.76% <0.00%> (+11.76%)	⬆️
pl_bolts/models/self_supervised/amdim/datasets.py	56.89% <0.00%> (+12.06%)	⬆️
... and 65 more

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