lib/plugins/tag/gist.js
function gistTag(args, content) {
  const id = args.shift();
  const file = args.length ? `?file=${args[0]}` : '';

  return `<script src="//gist.github.com/${id}.js${file}"></script>`;
}
function gistTag(args, content) {
  const id = args.shift();
  const file = args.length ? `?file=${args[0]}` : '';

  return `<script src="//gist.github.com/${id}.js${file}"></script>`;
}
Gist tag

Syntax:
{% gist gist_id [filename] %}