execPromise for casperjs

execPromise.js

var require = patchRequire(require);
var cp = require('child_process');
var Q = require('q');

module.exports = function(cmd, args) {
  var q = Q.defer();
  cp.execFile(cmd, args, null, function(err, stdout, stderr) {
    if (err) return q.reject(err);
    return q.resolve(stdout, stderr);
  });
  return q.promise;
};