Allow the .4w7 file type to be uploaded to the WordPress media library

functions.php

<?php
/**
 * Allow the .4w7 file type to be uploaded to the WordPress media library.
 * 
 * Ref: https://gist.github.com/om4james/9927208
 *
 * Put this snippet into a child theme's functions.php file
 */
function rasq_myme_types( $mime_types ){
	$mime_types['4w7'] = 'application/octet-stream';
	return $mime_types;
}
add_filter( 'upload_mimes', 'rasq_myme_types' );