Downgrade serde for better rust compatibility

src/tab.rs

@@ -2604,7 +2604,7 @@ mod tests {
     fn tab_click_double_opens_folder() -> io::Result<()> {
         let (fs, mut tab) = tab_click_new(NUM_FILES, NUM_NESTED, NUM_DIRS, NUM_NESTED, NAME_LEN)?;
         let path = fs.path();
-        
+
         // Simulate double clicking second directory
         debug!("Emitting double click Message::DoubleClick(Some(1))");
         tab.update(Message::DoubleClick(Some(1)), Modifiers::empty());