message: update on_demand_inputs invalidation
diff: @@ -38,7 +38,7 @@ struct MyDatabase { ... }
  impl FileWatcher for MyDatabase {
  fn watch(&self, path: &Path) { ... }
  fn did_change_file(&mut self, path: &Path) {
  - self.query_mut(ReadQuery).invalidate(path);
  + ReadQuery.in_db_mut(self).invalidate(path);
  }
  }
  ```
  