fix(markdown-it-anchor): Add aria-label in anchors

Author: ktquez

Diff for: config/chainMarkdown.js

@@ -0,0 +1,9 @@
+function chainMarkdown (config) {
+  config
+    .plugin('anchor')
+    .tap(([options]) => [
+      Object.assign(options, { permalinkAttrs: () => ({ 'aria-label': 'Anchor' }) })
+    ])
+}
+
+module.exports = chainMarkdown

Diff for: index.js

@@ -1,6 +1,8 @@
 const plugins = require('./config/plugins')
+const chainMarkdown = require('./config/chainMarkdown')
 
 module.exports = {
   extend: '@vuepress/theme-default',
-  plugins
+  plugins,
+  chainMarkdown
 }