Added require key in composer.json

composer.json

@@ -35,7 +35,9 @@
       }
     }
   ],
-  "require": {},
+  "require": {
+      "drupal/core": "^8.8 || ^9"
+  },
   "suggest": {
     "jackmoore/colorbox": "The Colorbox library is required to use the drupal/colorbox module."
   },