Merge #15577: Docs: Enable TLS in link to chris.beams.io

228e806 Enable TLS in link to chris.beams.io (JeremyRand)

Pull request description:

  This PR enables TLS in a documentation link to chris.beams.io, which improves security.  This change was originally part of bitcoin/bitcoin#13778 , which was closed for reasons unrelated to this change.

Tree-SHA512: 01f02031b39ebdaa7fc1859befde7e3bfff105892a8b9e1737ff94741599c6c5936eff53871e5e3560931512c9b7a4ea34f48d8555b583d232c90c2ca6d4d776

Author: jonasschnelli

CONTRIBUTING.md

@@ -62,7 +62,7 @@ Commit messages should be verbose by default consisting of a short subject line
 paragraph(s), unless the title alone is self-explanatory (like "Corrected typo
 in init.cpp") in which case a single title line is sufficient. Commit messages should be
 helpful to people reading your code in the future, so explain the reasoning for
-your decisions. Further explanation [here](http://chris.beams.io/posts/git-commit/).
+your decisions. Further explanation [here](https://chris.beams.io/posts/git-commit/).
 
 If a particular commit references another issue, please add the reference. For
 example: `refs #1234` or `fixes #4321`. Using the `fixes` or `closes` keywords