code: function(file, args) {
      return new Promise(function(resolve, reject) {
        var child = spawn(file, args, { stdio: 'inherit' });
        child.on('error', reject);
        child.on('close', resolve);
      });
    }
docs: Spawn a process and return a promise.
  
  @param {string}   file Filename of the program to run.
  @param {string[]} args List of string arguments.
  @returns {Promise}