Update version

[YuanLiuuuuuu]

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Motivation

Please describe the motivation of this PR and the goal you want to achieve through this PR.

Modification

Please briefly describe what modification is made in this PR.

BC-breaking (Optional)

Does the modification introduce changes that break the backward compatibility of the downstream repositories?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here and update the documentation.

Checklist

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects, like MMDet or MMSeg.
• CLA has been signed and all committers have signed the CLA in this PR.

[fangyixiao18]

Please also update the version information in docs
Refer to #268

[codecov]

Codecov Report

Merging #296 (627f5c4) into dev_v0.9.0 (7516b5b) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@              Coverage Diff               @@
##           dev_v0.9.0     #296      +/-   ##
==============================================
+ Coverage       71.98%   72.01%   +0.02%     
==============================================
  Files             120      120              
  Lines            4698     4702       +4     
  Branches          757      757              
==============================================
+ Hits             3382     3386       +4     
  Misses           1162     1162              
  Partials          154      154              

Flag	Coverage Δ
unittests	72.01% <100.00%> (+0.02%)	⬆️

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Impacted Files	Coverage Δ
mmselfsup/__init__.py	90.90% <100.00%> (+1.25%)	⬆️
mmselfsup/version.py	61.53% <100.00%> (ø)

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