Error 404 with bootstrap

Hello,
With your theme in firefox, i have a 404 error message on console :
“Erreur dans les liens source : request failed with status 404
URL de la ressource : https://www.cyanidevf.fr/wp-content/themes/buildr/assets/lib/bootstrap/bootstrap.min.css?ver=1.3.1”

Can u tell me how i can stop it ?
I think the theme need an update for last wordpress versions but maybe another solution is possible !

Thanks.