Updated latest Godot version (3.1) in README.md

Author: t-karcher

README.md

@@ -6,7 +6,7 @@ be used with [Godot Engine](https://godotengine.org), the open source
 
 ## Important note
 
-- The `master` branch is compatible with the latest Godot version (currently 3.0).
+- The `master` branch is compatible with the latest Godot version (currently 3.1).
 - Use the appropriate branch for your Godot version, such as the
   [`2.1`](https://github.com/godotengine/godot-demo-projects/tree/2.1) branch
   for Godot 2.1.x.