修改d.ts中的类名,并添加全局方法的d.ts定义

types/menu.d.ts

@@ -2,7 +2,7 @@
 // Project: https://github.com/iview/iview
 // Definitions by: yangdan
 // Definitions: https://github.com/yangdan8/iview.git
-import Vue, { VNode } from "vue";
+import Vue, { VNode } from 'vue';
 
 export declare class Menu extends Vue {
   /**
@@ -73,7 +73,7 @@ export declare class MenuItem extends Vue {
   target?: '_blank' | '_self' | '_parent' | '_top';
 }
 
-export declare class Submenu extends Vue {
+export declare class MenuSub extends Vue {
   /**
    * 子菜单的唯一标识，必填
    */