Hello,

when using Google Charts as an engine, links to generate the image do not switch to https:// schema, leading to warnings in browsers that the page is in "mixed mode" (ie some elements are loaded over plain http).

It seems to be an edge case for the first time load of each QR code, since further calls appear to use a cached image, but in the case where the generation URL is cached by external caches etc you might find yourself using the external url more than required.

I imagine that the possible solutions would be to either :
* patch the generation process so that only the local image is ever served or
* patch the serving process to use schema-less urls ( instead of http://example.com use //example.com )

obviously, the better but more extensive change would be the first one. What are your thoughts on this?