fix external URLs in navbar

doks-theme/_includes/site-header.html

@@ -23,7 +23,7 @@
 					{% if site.doks.header.nav %}
 						<ul class="site-header__nav hidden-xs">
 							{% for item in site.doks.header.nav %}
-								<li><a href="{% if jekyll.environment == 'production' %}{{ site.doks.baseurl }}{% endif %}{{ item.item_url }}">{{ item.item_name }}</a></li>
+								<li><a href="{% if jekyll.environment == 'production' and not item.external_url %}{{ site.doks.baseurl }}{% endif %}{{ item.item_url }}">{{ item.item_name }}</a></li>
 							{% endfor %}
 						</ul><!-- /.site-header__nav -->
 						<button class="offcanvas-toggle visible-xs">