Switch license to GPLv3 or later

README.md

@@ -7,8 +7,9 @@
 Copyright (c) 2019-2020 OpenRS2 Authors
 
 OpenRS2 Parent is free software: you can redistribute it and/or modify it under
-the terms of version 3.0 of the GNU General Public License as published by the
-Free Software Foundation.
+the terms of the GNU General Public License as published by the Free Software
+Foundation, either version 3 of the License, or (at your option) any later
+version.
 
 OpenRS2 Parent is distributed in the hope that it will be useful, but WITHOUT
 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS

pom.xml

@@ -17,7 +17,7 @@
   </organization>
   <licenses>
     <license>
-      <name>GNU General Public License v3.0</name>
+      <name>GNU General Public License v3.0 or later</name>
       <url>https://www.gnu.org/licenses/gpl-3.0.txt</url>
     </license>
   </licenses>