[Fix] Read in rb mode then decode

[wangruohui]

On Windows :

with open("some_file", r) as f:
    f.read()

will decode the content of the file based on windows's system language setting.

Using rb mode then decode within python will force using utf-8.

note: the ruby precommit hook does not work on windows and I will recover it when everything other is good before actual merge.

[codecov]

Codecov Report

Merging #983 (7fe987f) into master (841a078) will decrease coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #983      +/-   ##
==========================================
- Coverage   65.27%   65.19%   -0.09%     
==========================================
  Files         151      154       +3     
  Lines        9619     9911     +292     
  Branches     1741     1807      +66     
==========================================
+ Hits         6279     6461     +182     
- Misses       3017     3116      +99     
- Partials      323      334      +11     

Flag	Coverage Δ
unittests	65.19% <100.00%> (-0.09%)	⬇️

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

Impacted Files	Coverage Δ
mmcv/utils/config.py	89.85% <100.00%> (ø)
mmcv/runner/hooks/optimizer.py	17.74% <0.00%> (-6.01%)	⬇️
mmcv/runner/hooks/logger/pavi.py	70.58% <0.00%> (-4.86%)	⬇️
mmcv/ops/corner_pool.py	51.35% <0.00%> (-4.59%)	⬇️
mmcv/utils/testing.py	96.00% <0.00%> (-4.00%)	⬇️
mmcv/runner/base_module.py	75.67% <0.00%> (-3.12%)	⬇️
mmcv/runner/fp16_utils.py	59.73% <0.00%> (-1.59%)	⬇️
mmcv/runner/hooks/logger/text.py	71.42% <0.00%> (-1.21%)	⬇️
mmcv/engine/test.py	26.04% <0.00%> (-0.85%)	⬇️
mmcv/utils/registry.py	98.31% <0.00%> (-0.02%)	⬇️
... and 18 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 841a078...7fe987f. Read the comment docs.

[ZwwWayne]

Kindly ping @wangruohui

[ZwwWayne]

@wangruohui ，lint failed. The comments are too long and need to be separated in two lines.