demo code not right on MAC

The demo code in README.md
`var cp = require('child_process'),
    psTree = require('ps-tree');

var child = cp.exec("node -e 'while (true);'", function () { /*...*/ });

psTree(child.pid, function (err, children) {
  cp.spawn('kill', ['-9'].concat(children.map(function (p) { return p.PID })));
});`

seems have no children in psTree callback on MAC platform. Node version is 10.16.3 LTS