Fix DiffNode.hashCode

Author: ibbem

src/main/java/org/variantsync/diffdetective/variation/diff/DiffNode.java

@@ -925,4 +925,9 @@ public String toString() {
         }
         return s;
     }
+
+    @Override
+    public int hashCode() {
+        return getID();
+    }
 }