Update build server URL to new organization namespace.

README.md

@@ -145,5 +145,5 @@ Also, please check out the [borgmatic development
 how-to](https://torsion.org/borgmatic/docs/how-to/develop-on-borgmatic/) for
 info on cloning source code, running tests, etc.
 
-<a href="https://build.torsion.org/witten/borgmatic" alt="build status">![Build Status](https://build.torsion.org/api/badges/witten/borgmatic/status.svg?ref=refs/heads/master)</a>
+<a href="https://build.torsion.org/borgmatic-collective/borgmatic" alt="build status">![Build Status](https://build.torsion.org/api/badges/borgmatic-collective/borgmatic/status.svg?ref=refs/heads/master)</a>
 

docs/how-to/develop-on-borgmatic.md

@@ -118,7 +118,7 @@ See the Black, Flake8, and isort documentation for more information.
 
 Each pull request triggers a continuous integration build which runs the test
 suite. You can view these builds on
-[build.torsion.org](https://build.torsion.org/witten/borgmatic), and they're
+[build.torsion.org](https://build.torsion.org/borgmatic-collective/borgmatic), and they're
 also linked from the commits list on each pull request.
 
 ## Documentation development