fix bug (#811)

[sunkafei]

• I have marked all applicable categories:
  • exception-raising fix
  • algorithm implementation fix
  • documentation modification
  • new feature
• I have reformatted the code using make format (required)
• I have checked the code using make commit-checks (required)
• If applicable, I have mentioned the relevant/related issue(s)
• If applicable, I have listed every items in this Pull Request below

Fix the bug#811.

I run the command make commit-checks but the get some errors which are not relevent to my code:

tianshou/policy/modelfree/trpo.py:131:29: B028 No explicit stacklevel keyword argument found. The warn method from the warnings module uses a stacklevel of 1 by default. This will only show a stack trace for the line on which the warn method is called. It is therefore recommended to use a stacklevel of 2 or greater to provide more information to the user.
                            warnings.warn(
                            ^

Just ignore it?

[Trinkle23897]

I’ll take it, don’t worry

[codecov-commenter]

Codecov Report

Merging #817 (746e2c5) into master (c8be85b) will increase coverage by 0.00%.
The diff coverage is 100.00%.

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@@           Coverage Diff           @@
##           master     #817   +/-   ##
=======================================
  Coverage   91.12%   91.12%           
=======================================
  Files          73       73           
  Lines        5082     5083    +1     
=======================================
+ Hits         4631     4632    +1     
  Misses        451      451           

Flag	Coverage Δ
unittests	91.12% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
tianshou/data/buffer/her.py	91.86% <100.00%> (+0.09%)	⬆️

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