SetYDataLabelPos is not updating Y data label position

Hello maintainers,

I tried different options like:

```php
$plot = new PHPlot();
$plot->SetYDataLabelPos('plotright');

$plot->SetYDataLabelPos('both');  // Would that duplicate the Y labels, right?
```

And the Chart renders correctly but always with the Y data labels on the left (as default)
Maybe it's me that I'm doing something wrong and that method is not for what I intend it is?