update version to 0.5.0

[Trinkle23897]

No description provided.

[codecov-commenter]

Codecov Report

Merging #826 (88606f2) into master (73600ed) will decrease coverage by 0.04%.
The diff coverage is 83.33%.

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@@            Coverage Diff             @@
##           master     #826      +/-   ##
==========================================
- Coverage   91.11%   91.07%   -0.04%     
==========================================
  Files          73       73              
  Lines        5085     5087       +2     
==========================================
  Hits         4633     4633              
- Misses        452      454       +2     

Flag	Coverage Δ
unittests	91.07% <83.33%> (-0.04%)	⬇️

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Impacted Files	Coverage Δ
tianshou/env/venvs.py	89.38% <81.81%> (-0.96%)	⬇️
tianshou/__init__.py	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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