docs: Fix two permanent redirects

Courtesy of `sphinx-build -b linkchecker doc`

Signed-off-by: Christian Decker <decker.christian@gmail.com>

CHANGELOG.md

@@ -1,8 +1,8 @@
 # Changelog
 All notable changes to this project will be documented in this file.
 
-The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
-and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]