feat(Parser): Add support for parsing subtitle for Shelf (#792)

src/parser/classes/Shelf.ts

@@ -13,6 +13,7 @@ export default class Shelf extends YTNode {
   icon_type?: string;
   menu?: YTNode | null;
   play_all_button?: Button | null;
+  subtitle?: Text;
 
   constructor(data: RawNode) {
     super();
@@ -35,5 +36,9 @@ export default class Shelf extends YTNode {
     if (Reflect.has(data, 'playAllButton')) {
       this.play_all_button = Parser.parseItem(data.playAllButton, Button);
     }
+
+    if (Reflect.has(data, 'subtitle')) {
+      this.subtitle = new Text(data.subtitle);
+    }
   }
 }