Fixed the link of posts' nav-button.

_includes/related-posts.html

@@ -50,7 +50,7 @@
       {% assign index = data[1] | plus: 0 %}
       {% assign post = site.posts[index] %}
       <div class="card">
-        <a href="{{ post.url }}">
+        <a href="{{ post.url | relative_url }}">
           <div class="card-body">
             <span class="timeago small">
                 {{ post.date | date: POST_DATE }}