calls.go
func (c *CallService) Hangup(sid string) (*Call, error) {
	data := url.Values{}
	data.Set("Status", string(StatusCompleted))
	return c.Update(context.Background(), sid, data)
}
func (c *CallService) Hangup(sid string) (*Call, error) {
	data := url.Values{}
	data.Set("Status", string(StatusCompleted))
	return c.Update(context.Background(), sid, data)
}
// Hang up an in-progress call.