bump copyright year

Author: Vladimir Kotal

opengrok-indexer/src/main/java/org/opengrok/indexer/index/IndexDatabase.java

@@ -18,7 +18,7 @@
  */
 
 /*
- * Copyright (c) 2008, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2008, 2020, Oracle and/or its affiliates. All rights reserved.
  * Portions Copyright (c) 2017, 2020, Chris Fraire <[email protected]>.
  */
 package org.opengrok.indexer.index;