Allow HTTPS download of code

Chrome complains of the bookmarklet with the following error:

    [blocked] The page at 'https://trello.com/b/...' was loaded over HTTPS, but ran insecure content from 'http://yobriefca.se/trello-cards/trello-cards.css': this content should also be loaded over HTTPS.

Downloading the bookmarklet with `//yobriefca.se` instead of `http://yobriefca.se` will use HTTP/HTTPS as needed.  However, for it to work you would need to enable HTTPS on your webserver.

Right now the bookmarklet is non-functional in chrome.