Add missing comma

plugins.json

@@ -15,7 +15,7 @@
       "Main": "https://assets.hongkiat.com/uploads/automated-php-test/tdd-example.jpg",
       "Alternative": "https://i.stack.imgur.com/mCYvN.png"
     }
-  }
+  },
   "Plex Libraries": {
     "author": "TehMuffinMoo",
     "category": "Library Management",