code: function changeConfig(oldConfig, newConfig) {
    invariant(isObject(oldConfig), 'Old config is not valid');
    invariant(isObject(newConfig), 'Config is not valid');
  
    if (newConfig.host) {
      var host = newConfig.host;
      var prefix = '';
  
      if (host.indexOf('http://') < 0 && host.indexOf('https://') < 0) {
        prefix += 'http://';
      }
  
      oldConfig.host = prefix + newConfig.host;
    }
  
    if (newConfig.port) {
      oldConfig.port = newConfig.port;
    }
  }
docs: Updates a config object
  @param  {Object}  oldConfig  Old configuration object
  @param  {Object}  newConfig  New configuration object
  @return {Undefined}