Update dropdown-button.md

[nicoklaxit]

First of all, thank you for your contribution! 😄

New feature please send pull request to feature branch, and rest to master branch.
Pull request will be merged after one of collaborators approve.
Please makes sure that these form are filled before submitting your pull request, thank you!

[中文版模板 / Chinese template]

This is a ...

• New feature
• Bug fix
• Site / document update
• Component style update
• TypeScript definition update
• Refactoring
• Code style optimization
• Branch merge
• Other (about what?)

What's the background?

1. Describe the source of requirement.
   handleMenuClick is called instead of handleButtonClick
2. Resolve what problem.
3. Related issue link.

API Realization (Optional if not new feature)

1. Basic thought of solution and other optional proposal.
2. List final API realization and usage sample.
3. GIF or snapshot should be provided if includes UI/interactive modification.

What's the effect? (Optional if not new feature)

1. Does this PR affect user? Which part will be affected?
2. What will say in changelog?
3. Does this PR contains potential break change or other risk?

Changelog description (Optional if not new feature)

1. English description
2. Chinese description (optional)

Self Check before Merge

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed

Additional Plan? (Optional if not new feature)

If this PR related with other PR or following info. You can type here.

[netlify]

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Building with commit edf1105

https://app.netlify.com/sites/ant-desing-vue/deploys/5cc8786c0eead4000961dabe

[codecov]

Codecov Report

Merging #742 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #742   +/-   ##
=======================================
  Coverage   87.27%   87.27%           
=======================================
  Files         145      145           
  Lines        4816     4816           
  Branches     1419     1419           
=======================================
  Hits         4203     4203           
  Misses        570      570           
  Partials       43       43

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[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.