fix: assets of document

frontend/app_flowy/packages/flowy_editor/pubspec.yaml

@@ -24,11 +24,11 @@ dev_dependencies:
 
 # The following section is specific to Flutter packages.
 flutter:
-
   # To add assets to your package, add an assets section, like this:
   assets:
     - assets/images/uncheck.svg
     - assets/images/
+    - assets/document.json
   #   - images/a_dot_burr.jpeg
   #   - images/a_dot_ham.jpeg
   #