remove unneeded mut ref

src/logic/future_moves.rs

@@ -362,7 +362,7 @@ impl FutureMoves {
                     continue;
                 }
                 m.is_trimmed = true;
-                m.sort_children(&mut self.arena);
+                m.sort_children(&self.arena);
                 if m.children.len() > self.config.top_k_children {
                     let drained = m.children.drain(self.config.top_k_children..);
                     for idx in drained {