Image is loaded insecurely

[camelid]

Firefox warns that the connection to the site is insecure because of images. I believe this is caused by the Rust logo image, which is being loaded from http://www.rust-lang.org/logos/rust-logo-256x256-blk.png (note the protocol). This might be fixed by changing http to https in the image src.

It's not a big deal, but it would be nice if it were shown as secure :)

Originally opened at nrc/rustaceans.org#647.