fix($theme-default): close dropdown on mouseout (fix #2227) (#2303)

Author: Mister-Hope

packages/@vuepress/theme-default/components/DropdownLink.vue

@@ -124,6 +124,7 @@ export default {
     border none
     font-weight 500
     color $textColor
+    pointer-events none
     &:hover
       border-color transparent
     .arrow