Sitemap shows http instead of https - rest of site fine

Happy almost 2018!

I’ve got a slight issue with the sitemap showing all the links as http when the site is strictly https. This wasn’t happening in stage so I think its something in the live environment (cloudflare possibly) but as this “wrong” url can confuse google I’d like to see if I can fix it - rest of the site like canonical url is fine.

Looking at the sitemap plugin it looks like this is the culprit {{uri.rootUrl(true)}}
What is the root of uri ?