Bump version to v3.1.2

Change-Id: I7d0dbd5567103c293305284715ea59c2bedb8f60
diff --git a/build.gradle b/build.gradle
index 1aa733d..2b3bb08 100644
--- a/build.gradle
+++ b/build.gradle
@@ -5,4 +5,4 @@
 }
 
 // Zentrale Projektversion für korapxmltool
-version = '3.1.1'
+version = '3.1.2'