Update to rust 2021

server/src/routes/api/category.rs

@@ -101,7 +101,7 @@ pub fn set_parent(
         }
 
         // this also makes sure that parent exists
-        let parent = category::get(&categories_tree, &&next_parent_id)?;
+        let parent = category::get(&categories_tree, &next_parent_id)?;
 
         match parent.parent {
             Some(grandparent_id) => next_parent_id = grandparent_id,