Menu: compensate for Vue regression

packages/menu/src/menu-mixin.js

 export default {
-  inject: ['rootMenu'],
   computed: {
     indexPath() {
       var path = [this.index];
@@ -12,6 +11,16 @@ export default {
       }
       return path;
     },
+    rootMenu() {
+      var parent = this.$parent;
+      while (
+        parent &&
+        parent.$options.componentName !== 'ElMenu'
+      ) {
+        parent = parent.$parent;
+      }
+      return parent;
+    },
     parentMenu() {
       let parent = this.$parent;
       while (

packages/menu/src/menu.vue

 <template>
   <el-menu-collapse-transition>
     <ul class="el-menu"
-      :key="collapse"
+      :key="+collapse"
       :class="{
         'el-menu--horizontal': mode === 'horizontal',
         'el-menu--dark': theme === 'dark',