fix(types): missing ariaLabel at default theme config

Author: ulivz

packages/@vuepress/types/src/theme-default.ts

@@ -262,6 +262,10 @@ export type DefaultThemeConfig = {
    * Locale's select text.
    */
   selectText?: string;
+  /**
+   * aria label 
+   */
+  ariaLabel?: string;
   /**
    * Options for  @vuepress/plugin-active-header-links.
    */