[Docs]Updated master branch to main

[rtcms]

Ref - https://about.gitlab.com/blog/2021/03/10/new-git-default-branch-name/

Check List

Please read and check followings before submitting a PR.

• [ ] I want to publish my theme on Hexo official website.
  • [ ] I have read the theme publishing doc.
  • [ ] name is unique.
  • [ ] link URL is correct.
  • [ ] preview URL is correct.
  • [ ] preview URL web site is rendered correctly.
  • [ ] Add a screenshot to source/themes/screenshots.
  • [ ] Screenshot filename is same as value of name.
  • [ ] Screenshot size is 800 * 500.
  • [ ] Screenshot file format is png.
• [ ] I want to publish my plugin on Hexo official website.
  • [ ] I have read the plugin publishing doc.
  • [ ] name is unique.
  • [ ] link URL is correct.
• [ ] Others (Update, fix, translation, etc...)
  • Languages:
  • [ ] en English
  • [ ] ko Korean
  • [ ] pt-br Brazilian Portuguese
  • [ ] ru Russian
  • [ ] th Thai
  • [ ] zh-cn simplified Chinese
  • [ ] zh-tw traditional Chinese

[github-actions[bot]]

Theme name validation passed. Theme thumbnails validation completed.

[jiangtj]

It depends on whether your project‘s default branch is main. As far as I know, most people initialize hexo projects through hexo init and create git repo through git init. And at present, the default branch of git is still master.

[uiolee]

after #1785, branch has been removed