code: func (c *Client) ConfigVarUpdate(appIdentity string, options map[string]*string, message string) (map[string]string, error) {
  	rh := RequestHeaders{CommitMessage: message}
  	var configVarRes map[string]string
  	return configVarRes, c.PatchWithHeaders(&configVarRes, "/apps/"+appIdentity+"/config-vars", options, rh.Headers())
  }
docs: // Update config-vars for app. You can update existing config-vars by setting
  // them again, and remove by setting it to nil.
  //
  // appIdentity is the unique identifier of the ConfigVar's App. options is the
  // hash of config changes – update values or delete by seting it to nil.