docs: Update arguments of GAN

[akihironitta]

What does this PR do?

Fixes docs for GAN which was not updated in #206.

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[codecov]

Codecov Report

Merging #333 into master will increase coverage by 0.20%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #333      +/-   ##
==========================================
+ Coverage   82.04%   82.24%   +0.20%     
==========================================
  Files          98       98              
  Lines        5492     5492              
==========================================
+ Hits         4506     4517      +11     
+ Misses        986      975      -11     

Flag	Coverage Δ
cpu	24.24% <ø> (ø)
pytest	24.24% <ø> (ø)
unittests	81.62% <ø> (+0.20%)	⬆️

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

Impacted Files	Coverage Δ
pl_bolts/models/gans/basic/basic_gan_module.py	95.34% <ø> (ø)
...l_bolts/models/rl/vanilla_policy_gradient_model.py	94.64% <0.00%> (+2.67%)	⬆️
pl_bolts/optimizers/lars_scheduling.py	95.74% <0.00%> (+17.02%)	⬆️

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[Borda]

good catch