Clarified license definition as GPL 2.0 or later is supported

composer.json

@@ -2,7 +2,7 @@
     "name": "engelsystem/engelsystem",
     "description": "Shift planning system for chaos events",
     "type": "project",
-    "license": "GPL-2.0",
+    "license": "GPL-2.0-or-later",
     "authors": [
         {
             "name": "msquare",

package.json

@@ -4,7 +4,7 @@
   "main": "index.js",
   "repository": "https://github.com/engelsystem/engelsystem.git",
   "author": "https://github.com/engelsystem/engelsystem/contributors",
-  "license": "GPL-2.0-only",
+  "license": "GPL-2.0-or-later",
   "scripts": {
     "build": "npm run -s build:clean && NODE_ENV=production run-p build:webpack",
     "build:clean": "rimraf public/assets",