calls.go
func (c *CallService) Update(ctx context.Context, sid string, data url.Values) (*Call, error) {
	call := new(Call)
	err := c.client.UpdateResource(ctx, callsPathPart, sid, data, call)
	return call, err
}
func (c *CallService) Update(ctx context.Context, sid string, data url.Values) (*Call, error) {
	call := new(Call)
	err := c.client.UpdateResource(ctx, callsPathPart, sid, data, call)
	return call, err
}
// Update the call with the given data. Valid parameters may be found here:
// https://www.twilio.com/docs/api/rest/change-call-state#post-parameters