tweak: noopener/noreferrer for default theme links

Author: yyx990803

Diff for: lib/default-theme/NavLinks.vue

@@ -13,7 +13,7 @@
       :href="githubLink"
       class="github-link"
       target="_blank"
-      rel="noopener">
+      rel="noopener noreferrer">
       GitHub
       <OutboundLink/>
     </a>

Diff for: lib/default-theme/Page.vue

@@ -2,7 +2,7 @@
   <div class="page">
     <Content :custom="false"/>
     <div class="content edit-link" v-if="editLink">
-      <a :href="editLink" target="_blank">Edit this page</a>
+      <a :href="editLink" target="_blank" rel="noopener noreferrer">Edit this page</a>
       <OutboundLink/>
     </div>
     <div class="content page-nav" v-if="prev || next">