docs: function _spawn(mvn, args) {
    const spawn = require('child_process').spawn;
    // Command to be executed.
    let cmd = mvn.options.cmd || mvnw(mvn.options.cwd) || 'mvn';
    return new Promise((resolve, reject) => {
      if (isWin) {
        args.unshift(cmd);
        args.unshift('/c'),
        args.unshift('/s');
        cmd = process.env.COMSPEC || 'cmd.exe';
      }
      const proc = spawn(cmd, args, { 'cwd': mvn.options.cwd });
      proc.on('error', reject);
      proc.on('exit', (code, signal) => {
        if (code !== 0) {
          reject({ 'code': code, 'signal': signal });
        } else {
          resolve();
        }
      });
      proc.stdout.on('data', process.stdout.write.bind(process.stdout));
      proc.stderr.on('data', process.stderr.write.bind(process.stderr));
    });
  }