fix: 当使用APP_ROOT时，在github编辑此页的路径问题

[MrSeaWave]

🤔 这个变动的性质是？/ What is the nature of this change?

• 新特性提交 / New feature
• bug 修复 / Fix bug
• 样式优化 / Style optimization
• 代码风格优化 / Code style optimization
• 性能优化 / Performance optimization
• 构建优化 / Build optimization
• 网站、文档、Demo 改进 / Website, documentation, demo improvements
• 重构代码或样式 / Refactor code or style
• 测试相关 / Test related
• 其他 / Other

🔗 相关 Issue / Related Issue

856

💡 需求背景和解决方案 / Background or solution

meta.filePath取自path.relative(process.cwd(), this.data('fileAbsPath') 而不是 path.relative(ctx.umi?.cwd || process.cwd(), this.data('fileAbsPath'))

📝 更新日志 / Changelog

Language	Changelog
🇺🇸 English	when use APP_ROOT，fix Edit this doc on GitHub link
🇨🇳 Chinese	修复当设定APP_ROOT 时，Edit this doc on GitHub指向问题

[github-actions]

🎊 PR Preview has been successfully built and deployed to https://dumi-preview-pr-857.surge.sh

[github-actions]

🎊 PR Mobile Preview has been successfully built and deployed to https://dumi-mobile-preview-pr-857.surge.sh

[PeachScript]

+1

[codecov]

Codecov Report

Merging #857 (81cf69d) into master (57d4133) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #857      +/-   ##
==========================================
- Coverage   94.61%   94.61%   -0.01%     
==========================================
  Files         112      112              
  Lines        2581     2580       -1     
  Branches      826      825       -1     
==========================================
- Hits         2442     2441       -1     
  Misses        135      135              
  Partials        4        4              

Impacted Files	Coverage Δ
...ackages/preset-dumi/src/transformer/remark/meta.ts	100.00% <100.00%> (ø)

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[PeachScript]

project coverage 是代码行数变少导致，PR 合并