docs: fix broken links

[suzuki-shunsuke]

What type of PR is this?

(REQUIRED)

• documentation

What this PR does / why we need it:

(REQUIRED)

This pull request fixes some broken (404) links.

Which issue(s) this PR fixes:

(REQUIRED)

This pull request is related to #1939 , but this pull request doesn't resolve the issue completely.

Special notes for your reviewer:

(fill-in or delete this section)

Testing

(fill-in or delete this section)

Release Notes

(REQUIRED)

[suzuki-shunsuke]

Some links are still broken, but I'm not sure how we should fix them.

$ git ls-files | grep -E "\.md$" | xargs lychee --max-concurrency 10 -a 429
  247/247 ━━━━━━━━━━━━━━━━━━━━ Finished extracting links                                                                                       Issues found in 2 inputs. Find details below.

[docs/CHANGELOG.md]:
✗ [404] https://github.com/lynncyrin/ | Failed: Network error: Not Found
✗ [404] https://github.com/urfave/cli/compare/v1.22.4...v1 | Failed: Network error: Not Found
✗ [404] https://github.com/masonj188 | Failed: Network error: Not Found
✗ [404] https://github.com/urfave/891 | Failed: Network error: Not Found

[docs/CONTRIBUTING.md]:
✗ [404] https://github.com/urfave/cli/tree/v1 | Failed: Network error: Not Found

🔍 247 Total (in 12s) ✅ 237 OK 🚫 6 Errors 💤 4 Excluded
💡 There were issues with GitHub URLs. You could try setting a GitHub token and running lychee again.%

[Juneezee]

Thanks for submitting a PR 👍