allow crud v6 and dev

Author: tabacitu

composer.json

@@ -12,7 +12,7 @@
     "homepage": "https://github.com/laravel-backpack/filemanager",
     "keywords": ["Laravel", "FileManager"],
     "require": {
-        "backpack/crud": "^5.0",
+        "backpack/crud": "^5.0|^6.0|6.x-dev",
         "barryvdh/laravel-elfinder": "^0.5.0"
     },
     "require-dev": {