Bump version to v2.20

Change-Id: I581ace3cadc1c198d41e969eea2d89017b652e01
diff --git a/build.gradle b/build.gradle
index a45ca50..55172cb 100644
--- a/build.gradle
+++ b/build.gradle
@@ -5,4 +5,4 @@
 }
 
 // Zentrale Projektversion für korapxmltool
-version = '2.10'
+version = '2.20'