fix invalid link

[qingyun-wu]

Why are these changes needed?

Fix invalid link

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov-commenter]

Codecov Report

Merging #20 (0051570) into main (6f54631) will increase coverage by 0.29%.
Report is 10 commits behind head on main.
The diff coverage is 92.30%.

@@            Coverage Diff             @@
##             main      #20      +/-   ##
==========================================
+ Coverage   34.22%   34.51%   +0.29%     
==========================================
  Files          17       17              
  Lines        1911     1921      +10     
  Branches      416      420       +4     
==========================================
+ Hits          654      663       +9     
  Misses       1207     1207              
- Partials       50       51       +1     

Flag	Coverage Δ
unittests	34.46% <92.30%> (+0.29%)	⬆️

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Files	Coverage Δ
autogen/code_utils.py	45.53% <92.30%> (+2.19%)	⬆️