Fix from_argparse_args

[ethanwharris]

What does this PR do?

Fixes #379

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[codecov]

Codecov Report

Merging #380 (3002ba3) into master (28b5a1e) will increase coverage by 0.00%.
The diff coverage is 92.30%.

@@           Coverage Diff           @@
##           master     #380   +/-   ##
=======================================
  Coverage   89.44%   89.45%           
=======================================
  Files          80       80           
  Lines        4180     4192   +12     
=======================================
+ Hits         3739     3750   +11     
- Misses        441      442    +1     

Flag	Coverage Δ
unittests	89.45% <92.30%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
flash/core/trainer.py	87.50% <92.30%> (+0.73%)	⬆️

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