Update composer.json

composer.json

@@ -3,7 +3,7 @@
   "type": "typo3-cms-extension",
   "description": "RTE integration of TinyMCE for TYPO3.",
   "homepage": "https://www.sgalinski.de",
-  "license": ["GPL-2.0+"],
+  "license": "GPL-2.0+",
   "version": "2.2.1",
   "support": {
     "issues": "https://forge.typo3.org/projects/extension-tinymce4_rte"