code: function installVer(name, ver, dir) {
          var _child$spawnSync2 = _child_process2['default'].spawnSync(npmCommand, ['install', name + '@' + ver], { cwd: dir });
  
          var error = _child$spawnSync2.error;
  
          if (error) throw error;
      }
docs: install package via npm
  
  @param {String} [name] published package name
  @param {String} [ver] install version
  @param {String} [dir] install directory
  @public