update argument name

src/app/browser/header/widget.rs

@@ -6,10 +6,10 @@ pub struct Widget {
 
 impl Widget {
     // Construct
-    pub fn new(tray: &Box, title_widget: Option<&Box>) -> Self {
+    pub fn new(pack_start: &Box, title_widget: Option<&Box>) -> Self {
         let gobject = HeaderBar::builder().build();
 
-        gobject.pack_start(tray);
+        gobject.pack_start(pack_start);
         gobject.set_title_widget(title_widget);
 
         Self { gobject }