Footer: Replaced `{{ base_url }}{{ entry.url }}` by `{{ entry.url | relative_url }}`

_includes/footer.html

@@ -22,7 +22,7 @@
             </a>
 
             {% for entry in site.data.navigation.footer %}
-                <a href="{{ base_url }}{{ entry.url }}" class="btn btn-primary">
+                <a href="{{ entry.url | relative_url }}" class="btn btn-primary">
                     {{ entry.title }}
                 </a>
             {% endfor %}