function notFound( request, response ) {
	debug( 'Sending 404 response...' );
	response.statusCode = 404;
	response.setHeader( 'Content-Type', 'text/plain' );
	response.setHeader( 'Content-Length', message.length );
	response.end( message );
}
Returns a `404` response.

@private
@param {IncomingMessage} request - HTTP request object
@param {ServerResponse} response - HTTP response object