[Fix] use LooseVersion for version checking

[kennymckormick]

Motivation

Origin version checking compares 2 strings, which leads to bugs like '0.8.0' > '0.10.0'

Modification

Use LooseVersion for Version Checking.

[kennymckormick]

@zhouzaida

[codecov]

Codecov Report

Merging #1158 (5862fee) into master (76d9bf1) will increase coverage by 0.02%.
The diff coverage is 36.36%.

❗ Current head 5862fee differs from pull request most recent head 9b2f102. Consider uploading reports for the commit 9b2f102 to get more accurate results

@@            Coverage Diff             @@
##           master    #1158      +/-   ##
==========================================
+ Coverage   67.96%   67.98%   +0.02%     
==========================================
  Files         159      159              
  Lines       10416    10424       +8     
  Branches     1896     1896              
==========================================
+ Hits         7079     7087       +8     
  Misses       2969     2969              
  Partials      368      368              

Flag	Coverage Δ
unittests	67.98% <36.36%> (+0.02%)	⬆️

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

Impacted Files	Coverage Δ
mmcv/parallel/distributed.py	22.44% <20.00%> (+1.61%)	⬆️
mmcv/runner/fp16_utils.py	58.38% <25.00%> (+0.26%)	⬆️
mmcv/ops/saconv.py	88.70% <33.33%> (+0.18%)	⬆️
mmcv/cnn/bricks/activation.py	88.00% <50.00%> (+0.50%)	⬆️
mmcv/parallel/distributed_deprecated.py	67.39% <50.00%> (+0.72%)	⬆️
mmcv/runner/dist_utils.py	50.49% <50.00%> (+0.49%)	⬆️
mmcv/runner/hooks/logger/tensorboard.py	36.36% <50.00%> (+1.98%)	⬆️
mmcv/runner/hooks/optimizer.py	17.29% <50.00%> (+0.62%)	⬆️

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[zhouzaida]

LGTM