"View this file on GitHub" links of the generated document don't wok when the default branch is "main"

[kmyk]

Description

The branch name master is hard-coded in the Jekyll template. When users use main for the default branch, this doesn't work.

verification-helper/onlinejudge_verify_resources/_includes/document_header.html

Line 6 in f675f8b

<li><a href="{{ site.github.repository_url }}/blob/master/{{ page.data.path }}">View this file on GitHub</a></li>

Note: the site.github doesn't have something like default_branch now (#365).