chore(docs): fix broken upgrade link in banner (#2091)

Author: dreamorosi

docs/overrides/main.html

@@ -8,6 +8,6 @@
 {% endblock %}
 
 {% block announce %}
-Version 2 is coming soon 🔥 Check out the <a href="{{ '../' ~ base_url ~ '/upgrade' }}">upgrade guide</a> to see what's
-new.
+Version 2 is coming soon 🔥 Check out the <a href="{{ '../' ~ base_url ~ '/latest/upgrade' }}">upgrade guide</a> to see
+what's new.
 {% endblock %}