code: func (h *Client) CacheBuster(cacheBuster string) *Client {
  	h.cacheBuster = cacheBuster
  	h.cacheBusterSet = true
  	return h
  }
docs: // Used to send a random number in GET requests to ensure browsers
  // and proxies don't cache hits. It should be sent as the final
  // parameter of the request since we've seen some 3rd party
  // internet filtering software add additional parameters to
  // HTTP requests incorrectly. This value is not used in reporting.