Change mmcv minimum version

[ckkelvinchan]

Motivation

As discussed in #376, _load_checkpoint_with_prefix is used in StyleGAN, but is not included in mmcv < 1.3.

Modification

This PR changes the minimum mmcv version specified in mmedit/__init__.py, from 1.0.2 to 1.3.

[codecov]

Codecov Report

Merging #378 (8ff559f) into master (2c21fa8) will increase coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head 8ff559f differs from pull request most recent head 7701c1a. Consider uploading reports for the commit 7701c1a to get more accurate results

@@            Coverage Diff             @@
##           master     #378      +/-   ##
==========================================
+ Coverage   80.30%   80.32%   +0.02%     
==========================================
  Files         184      184              
  Lines        9831     9831              
  Branches     1427     1427              
==========================================
+ Hits         7895     7897       +2     
+ Misses       1743     1742       -1     
+ Partials      193      192       -1     

Flag	Coverage Δ
unittests	80.30% <100.00%> (+0.01%)	⬆️

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Impacted Files	Coverage Δ
mmedit/__init__.py	73.68% <100.00%> (ø)
...ls/components/stylegan2/generator_discriminator.py	86.14% <0.00%> (+1.20%)	⬆️

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