Docs: Update some links

- https where possible
- Brack3t no longer has a web site

Author: medmunds

CHANGELOG.rst

@@ -6,7 +6,7 @@ Among other things, this means that minor updates (1.x to 1.y)
 should always be backwards-compatible, and breaking changes will
 always increment the major version number (1.x to 2.0).
 
-.. _semver: http://semver.org
+.. _semver: https://semver.org
 
 
 ..  This changelog is designed to be readable standalone on GitHub,

docs/contributing.rst

@@ -24,10 +24,9 @@ See the `contributor chart`_ for a list of some of the people who have helped
 improve Anymail.
 
 Anymail evolved from the `Djrill`_ project. Special thanks to the
-folks from `brack3t`_ who developed the original version of Djrill.
+folks from Brack3t who developed the original version of Djrill.
 
 .. _contributor chart: https://github.com/anymail/django-anymail/graphs/contributors
-.. _brack3t: http://brack3t.com/
 .. _Djrill: https://github.com/brack3t/Djrill