Update link to RFC3986

The previous link was a redirect to the new link.

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

Author: zecakeh

data/string-formats.yaml

@@ -60,4 +60,4 @@ mx-mxc-uri:
 
 uri:
   title: URI
-  url: http://tools.ietf.org/html/rfc3986
+  url: https://datatracker.ietf.org/doc/html/rfc3986