doc: fix the syntax of the show vnodes command

docs/en/12-taos-sql/24-show.md

@@ -363,7 +363,7 @@ Shows information about all vgroups in the system or about the vgroups for a spe
 ## SHOW VNODES
 
 ```sql
-SHOW VNODES [dnode_name];
+SHOW VNODES {dnode_id | dnode_endpoint};
 ```
 
 Shows information about all vnodes in the system or about the vnodes for a specified dnode.

docs/zh/12-taos-sql/24-show.md

@@ -306,7 +306,7 @@ SHOW [db_name.]VGROUPS;
 ## SHOW VNODES
 
 ```sql
-SHOW VNODES [dnode_name];
+SHOW VNODES {dnode_id | dnode_endpoint};
 ```
 
 显示当前系统中所有 VNODE 或某个 DNODE 的 VNODE 的信息。