Makes requests over HTTPS where possible

This will let the website run more smoothly when accessed over `https://` (which Github Pages [now supports](https://konklone.com/post/github-pages-now-supports-https-so-use-it) for `*.github.io` URLs).

I'm not sure whether this will actually work until it's merged -- in development, the congress-forms server's CORS whitelisting blocked me from fetching content, and I don't know whether the change in protocol will disrupt the CORS whitelisting.

Either way, it will only help -- the site's already not working over HTTPS. Still, I'd like @legind or @sinak or someone with server control to merge this one, and add `https://efforg.github.io` to the list of CORS whitelisted servers.