SSL check for javascript referencing sometimes failing

The javascript reference to static.addtoany.com/menu/page.js in addtoany_page_alter() checks for HTTPS on the server and changes the protocol to http or https based on that. We ran into an issue where this check was failing on our environment. This could be due to running Pound and Varnish running on that server. At any rate, a better method would probably be to use the agnostic // protocol, which will work for either http or https.