fix locale discovery by django app

src/paperless/urls.py

@@ -90,7 +90,7 @@ urlpatterns = [
 
     # Frontend assets TODO: this is pretty bad, but it works.
     path('assets/<path:path>',
-         RedirectView.as_view(url='/static/frontend/en-us/assets/%(path)s')),
+         RedirectView.as_view(url='/static/frontend/en-US/assets/%(path)s')),
     # TODO: with localization, this is even worse! :/
 
     # login, logout