Include bStats, Github Actions in changelog.

These should have been included in their respective commits, but they
didn't seem particularly interesting for end users at the time. Might as
well include them, though.

changelog.md

@@ -14,6 +14,10 @@ These changes will (most likely) be included in the next version.
 ### Added
 - It is now possible to write custom formulas for wave growth in Default Wave, swarm amounts in Swarm Waves, and boss health in Boss Waves, allowing for much more control and fine-tuning. The formulas support various session-related variables as well as various mathematical operators and functions. Formulas can be predefined as macros in the new `formulas.yml` file. Check the wiki for details.
 
+### Changed
+- bStats Metrics client updated to 2.2.1.
+- MobArena now uses Github Actions instead of Travis CI. This should make it easier to get development builds directly from Github for those interested.
+
 ### Fixed
 - Arena signs in unloaded or missing worlds no longer break the startup procedure. Sign data is stored in a new format that MobArena will automatically migrate to on a per-world basis during startup.