client.go
func (c *Client) TriggerMulti(channels []string, eventName string, data interface{}) (*BufferedEvents, error) {
	return c.trigger(channels, eventName, data, nil)
}
func (c *Client) TriggerMulti(channels []string, eventName string, data interface{}) (*BufferedEvents, error) {
	return c.trigger(channels, eventName, data, nil)
}
/*
The same as `client.Trigger`, except one passes in a slice of `channels` as the first parameter.
The maximum length of channels is 100.
	client.TriggerMulti([]string{"a_channel", "another_channel"}, "event", data)
*/