Fatal error

I tried to combine the theme of Sequel with the plugins of twenty fourteen. When I tried to work on the slider, I got this message: Fatal error: Call to undefined function wp_is_mobile() in /home/roadtr11/public_html/wp-content/plugins/fourteen-extended/inc/fourteenxt-customizer.php on line 633

I don’t have any access anymore to my website: http://road-tripping-europe.com. Please help me!

https://ww.wp.xz.cn/plugins/styles-twentyfourteen/