wp_enqueue_style not adding version

I am trying to add version to style.css file but its not adding version to style.css infact not adding version to any of css files. here's my code

wp_enqueue_style( 'twentyfifteen-style', get_template_directory_uri() . '/css/style.css', array(),'1.0','all');

Does any body knows what is the issue?

Thanks