function onClose( code, signal ) {
		debug( 'Child process closed. Code: %d. Signal: %s. pid: %d.', code, signal, child.pid );
		processExit( code, signal );
		if ( err ) {
			return clbk( err );
		}
		clbk( null, child.pid, script );
	}
Callback invoked upon child process close.

@private
@param {(number|null)} code - exit code
@param {(string|null)} signal - termination signal
@returns {void}