fix custom shiftwidth

[lambillda]

When expendtab is on and shiftwidth isn't 2, the sub-content will show wrong.

[mzlogin]

Would you please provider some test data?

For a long time, I have used the configuration of expandtab is on and shiftwidth is 4, and everything is ok.

[lambillda]

I check my .vimrc and found that I deleted the set shiftwidth option, so when expendtab is on 1 tab = 8 spaces, and I also do some test in my vim's markdown preview pluggin markdown-preview.nvim(unknow style, maybe Redcarpet?) and github's markdown preview(GFM style).

results:

markdown-preview.nvim

github

This is one space

• T1

• T2

  This is six spaces

• T1

• T2

  These are 2-5 spaces

• T1
• T2

• T1

  • T2

• T1

  • T2

• T1

  • T2

    I found that only when spaces between 2-5 could both show correct. So I misunderstand what's wrong, and I will change some codes and reopen the pull request.