Subject in header in _sidebar.md and Home.md should not have .md at the end

[kevin-lee]

The current pre-commit generates a subject_to_header value for a _sidebar.md file like

### [[☰|1.-About.md]] 1. About.md

1.-About.md is https://github.com/hybridgroup/GitHub-Wikifier/wiki/1.-About.md (<= Please click it to see what happens)
and it is redirected to https://raw.githubusercontent.com/wiki/hybridgroup/GitHub-Wikifier/1.-About.md which is a URL for a raw content.

So, to avoid this issue, the md extension should be removed.

Just like this one

### [[☰|1.-About]] 1. About