docs: fix typo `post` -> `port`

[wxsms]

Summary

Which package does this PR involve? (check one)

• [ ] root project
• [ ] vuepress-plugin-clean-urls
• [ ] vuepress-plugin-container
• [ ] vuepress-plugin-dehydrate
• [ ] vuepress-plugin-medium-zoom
• [ ] vuepress-plugin-named-chunks
• [ ] vuepress-plugin-nprogress
• [ ] vuepress-plugin-redirect
• [ ] vuepress-plugin-smooth-scroll
• [ ] vuepress-plugin-table-of-contents
• [ ] vuepress-plugin-typescript
• [ ] vuepress-plugin-zooming
• [ ] vuepress-mergeable
• [ ] vuepress-types
• [x] vuepress-plugin-serve

What kind of change does this PR introduce? (check at least one)

• [ ] Bugfix (fix)
• [ ] Feature (feat)
• [ ] Performance enhancement (perf)
• [ ] Code Style (style)
• [ ] Refactor (refactor)
• [x] Docs (docs)
• [ ] Build-related changes (build)
• [ ] CI-related changes (ci)
• [ ] Testing (test)
• [ ] Other, please describe:

Does this PR introduce a breaking change? (check one)

• [ ] Yes
• [x] No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• [ ] When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

Other information:

[wxsms]

I don't think that my little changes causing the build failed. It looks like it's failing since my fork.

[wxsms]

@meteorlxy may you explain why this closed?

[meteorlxy]

I did nothing on this PR. It was closed because the target branch was deleted. You can re-open it if you want

[wxsms]

@meteorlxy I have no access to edit the target branch or re-open. would you please give a help and merge this one? thank you. It's a simple typo fix.