WP Update Errors

hey Guys i tried to update WP to the latest version and all i get is the below

Fatal error: Cannot redeclare wp_is_mobile() (previously declared in /home/domain/public_html/wp-includes/vars.php:107) in /home/domain/public_html/wp-includes/vars.php on line 126

any one has an idea of what that could be?

please asdvice