chore: prep for beta.7 (#4377)

Author: imorland

composer.json

@@ -19,7 +19,7 @@
         }
     ],
     "require": {
-        "flarum/core": "^2.0.0-beta.6",
+        "flarum/core": "^2.0.0-beta.7",
         "pusher/pusher-php-server": "^7.2"
     },
     "require-dev": {