Make link in docs use HTTPS (#10130)

Fixes #10121

Signed-off-by: Rohan Sharma <rhnsharma5113@gmail.com>

changelog.d/10130.doc

+Make a link in docs use HTTPS. Contributed by @RhnSharma.

docs/turn-howto.md

@@ -4,7 +4,7 @@ This document explains how to enable VoIP relaying on your Home Server with
 TURN.
 
 The synapse Matrix Home Server supports integration with TURN server via the
-[TURN server REST API](<http://tools.ietf.org/html/draft-uberti-behave-turn-rest-00>). This
+[TURN server REST API](<https://tools.ietf.org/html/draft-uberti-behave-turn-rest-00>). This
 allows the Home Server to generate credentials that are valid for use on the
 TURN server through the use of a secret shared between the Home Server and the
 TURN server.