Add class and placeholder to name and email field of Wordpress comment template

comments.php

$fields =  array(
        'author' => '<ul class="row"><li class="col-sm-6"><label>' . '<input class="form-control" id="author" name="author" type="text" placeholder="' . esc_attr__( "Name", "text-domain" ) . '" value="' . esc_attr( $commenter['comment_author'] ) . '" size=""' . $aria_req . ' /></label></li>',
        'email'  => '<li class="col-sm-6"><label>' .  '<input class="form-control" name="email" type="text" placeholder="' . esc_attr__( "Email", "text-domain" ) . '" value="' . esc_attr(  $commenter['comment_author_email'] ) . '" size=""' . $aria_req . ' /></label></li>',

    );
    comment_form(array('fields'=>$fields));