mixed content warning because of image in <noscript>
mixed content warning because of image in <noscript>

Hi,

I'm maintainer of a [diaspora*](https://github.com/diaspora/diaspora) pod, which uses this gem for piwik integration.

Today I noticed, that I get a mixed content warning although all my images and ressources are embedded with https:// and all external images are proxied.

I noticed, that the <noscript> tag of piwik contains a http:// image and after I deactivated the piwik integration the mixed content warning dissappeared, so I guess [this template](https://github.com/maxwell/rack-piwik/blob/master/lib/rack/templates/sync.erb) is the reason why a warning appeared in first place.


I guess it would be best to inherit Piwik's default code with src="//url" instead of src="http://url"

Best
lub
maxwell/rack-piwik,maxwell/rack-piwik