Update changelog

Author: dvdoug

CHANGELOG.md

@@ -1,6 +1,8 @@
 # Changelog
 
 ## [3.x - Unreleased] - 2021-xx-xx
+
+## [3.9.4] - 2021-10-21
 ### Changed
 -  `psr/log` compatibility changed from `^1.0` to `^1.0||^2.0||^3.0`
 
@@ -479,8 +481,9 @@ Initial release
  - Experimental code to get a feel for how calculations can best be implemented
  - Only works if all items fit into a single box (so not production ready at all)
 
-[3.x - Unreleased]: https://github.com/dvdoug/BoxPacker/compare/3.9.3...3.x
+[3.x - Unreleased]: https://github.com/dvdoug/BoxPacker/compare/3.9.4...3.x
 
+[3.9.4]: https://github.com/dvdoug/BoxPacker/compare/3.9.3...3.9.4
 [3.9.3]: https://github.com/dvdoug/BoxPacker/compare/3.9.2...3.9.3
 [3.9.2]: https://github.com/dvdoug/BoxPacker/compare/3.9.1...3.9.2
 [3.9.1]: https://github.com/dvdoug/BoxPacker/compare/3.9.0...3.9.1