Fix EMNSIT download URL

[pmeier]

fixes #1296

@fmassa The link you provided works as drop-in replacement. The website looks official to me, since it comprises citing information and so on. Do you want me to include a comment why this does not link to the official dataset website?

[fmassa]

Thanks for the fix!

Can you update the comments with the place where you found the new URL from?

[codecov-io]

Codecov Report

Merging #1318 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #1318      +/-   ##
=========================================
+ Coverage   65.58%   65.6%   +0.01%     
=========================================
  Files          74      74              
  Lines        5786    5786              
  Branches      884     884              
=========================================
+ Hits         3795    3796       +1     
+ Misses       1726    1725       -1     
  Partials      265     265

Impacted Files	Coverage Δ
torchvision/datasets/mnist.py	51.7% <100%> (ø)	⬆️
torchvision/transforms/transforms.py	80.94% <0%> (-0.59%)	⬇️
torchvision/transforms/functional.py	71.38% <0%> (+1.15%)	⬆️

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