Upgrade shiki and vuepress plugins

Author: hustcer

.vuepress/styles/index.scss

@@ -82,6 +82,6 @@ html[data-theme='dark'] {
   h2.title a {
     color: #adb6be;
     font-weight: 500;
-    text-decoration: none;
+    text-decoration: underline;
   }
 }