`label_tag` for fieldset has no effect in Widget::Block

[tbe]

In the documentation for HTML::FormHandler::Widget::Block, the label_tag attributed is documented as:

Tag to use for the label. Default: 'span'; default for 'fieldset' is 'legend'.

As this is true for span, the tag legend is enforced for fieldset.

https://github.com/gshank/html-formhandler/blob/master/lib/HTML/FormHandler/Widget/Block.pm#L151

The documentation or the could should be fixed.