function onWrite( error ) {
		if ( error ) {
			debug( 'Encountered an error when writing bundle to file: %s', error.message );
			return cb( error );
		}
		debug( 'Successfully wrote bundle to file.' );
		cb();
	}
Callback invoked upon writing a file.

@private
@param {(Error|null)} error - error object
@returns {void}