Support HTTP/HTTPS loading when embed script '*disqus.com/embed.js'

I want to use this theme via HTTPS.

See also:
[Can Disqus be loaded via HTTPS? | DISQUS](https://help.disqus.com/customer/portal/articles/542119-can-disqus-be-loaded-via-https- "Can Disqus be loaded via HTTPS? | DISQUS")