code: func (h *Client) DataSource(dataSource string) *Client {
  	h.dataSource = dataSource
  	h.dataSourceSet = true
  	return h
  }
docs: // Indicates the data source of the hit. Hits sent from analytics.js
  // will have data source set to 'web'; hits sent from one of
  // the mobile SDKs will have data source set to 'app'.