fix printing link (#884)

Author: jaysa68

ocfweb/docs/templates/docs/lab.html

@@ -30,7 +30,7 @@
 
                 <p>
                     For details about printing in the lab, see
-                    <a href="{% url 'doc' 'services/lab/printing' %}">Printing</a>.
+                    <a href="{{ docs_url }}/services/lab/printing">Printing</a>.
                 </p>