[Fix] singan errors

[JiangongWang]

math.log(a, b) is equal to np.log(a)/np.log(b)

[codecov]

Codecov Report

Merging #192 (09455b6) into master (3cd123b) will increase coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #192      +/-   ##
==========================================
+ Coverage   75.52%   75.61%   +0.08%     
==========================================
  Files         127      128       +1     
  Lines        8814     8927     +113     
  Branches     1748     1781      +33     
==========================================
+ Hits         6657     6750      +93     
- Misses       1719     1728       +9     
- Partials      438      449      +11     

Flag	Coverage Δ
unittests	75.61% <ø> (+0.08%)	⬆️

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

Impacted Files	Coverage Δ
mmgen/datasets/singan_dataset.py	30.95% <ø> (ø)
...chitectures/biggan/generator_discriminator_deep.py	77.87% <0.00%> (-1.37%)	⬇️
...ls/architectures/biggan/generator_discriminator.py	77.72% <0.00%> (-1.30%)	⬇️
mmgen/models/architectures/biggan/modules.py	95.98% <0.00%> (-1.10%)	⬇️
...gen/models/architectures/biggan/biggan_snmodule.py	89.23% <0.00%> (ø)
mmgen/models/architectures/stylegan/mspie.py	91.58% <0.00%> (+0.99%)	⬆️

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