Replace mention of Travis with GitHub Action.

Author: EreMaijala

README.md

@@ -57,7 +57,7 @@ If you need to use the plugin without a KPZ package (e.g. to use a version clone
 
 ## Building a Release
 
-Travis will build the release provided the commit includes a suitable version tag:
+A GitHub Action will build the release provided the commit includes a suitable version tag:
 
 1. `git tag -a vX.Y.Z -m "Release X.Y.Z"` (Feel free to provide a longer message too, it's displayed on the Releases page)
 2. `git push --tags origin main`