Fix mixed-mode issues on https

[mattstratton]

when https://www.devopsdays.org is loaded, it has a mixed mode issue because of this resource:

http://maps.gstatic.com/intl/en_us/mapfiles/drag_cross_67_16.png

This is coming from Google, but I cannot figure out how to get it to load the SSL version of that. The maps API call seems to be configured properly for SSL.

This is a blocker for #642

[mattstratton]

Oof. @yvovandoorn seems to have found another reference at https://github.com/devopsdays/devopsdays-web/blob/master/layouts/shortcodes/event_map.html#L36

[mattstratton]

Fixed in #932