docs: function unreference() {
      var plugins = this._plugins
  
      Object.keys(plugins).forEach(function (name) {
          var plugin = plugins[ name ]
  
          // `unref()` is preferred
          if (typeof plugin.unref === 'function')
              plugin.unref()
          // if we cannot stop gracefully then destroy open
          // connections immediately
          else {
              // `destroy()` is required by `Plugin` base class,
              // so it's guaranteed that it exists
              plugin.destroy()
          }
      })
  
      // make it chainable
      return this
  }