patch 8.1.2243: typos in comments

Problem:    Typos in comments.
Solution:   Fix the typos. (Dominique Pelle, closes #5160)  Also adjust
            formatting a bit.
diff --git a/src/structs.h b/src/structs.h
index 265f0c4..124b059 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -3497,7 +3497,7 @@
 #ifdef FEAT_GUI_MAC
 //  MenuHandle	id;
 //  short	index;		    // the item index within the father menu
-    short	menu_id;	    // the menu id to which this item belong
+    short	menu_id;	    // the menu id to which this item belongs
     short	submenu_id;	    // the menu id of the children (could be
 				    // get through some tricks)
     MenuHandle	menu_handle;