Bump version to v3.1.0

Change-Id: Id6df65a1048375919a347f0af3af5f3bdbda22b7
diff --git a/build.gradle b/build.gradle
index 5574fe3..e3dea96 100644
--- a/build.gradle
+++ b/build.gradle
@@ -5,4 +5,4 @@
 }
 
 // Zentrale Projektversion für korapxmltool
-version = '3.1.0-rc1'
+version = '3.1.0'