Incorrect marker option name for adding class to icon

[mxgnr]

Hi there,

First of all, thank you for your work for this very useful plugin, it speeds up a lot leaflet integration :)

I may have found a bug in the marker shortcode attributes for adding a class to the image : it's actually set to iconClass in the plugin but leaflet does not add the new class, as the official documentation says to use className option instead (https://leafletjs.com/reference-1.7.1.html#icon-classname). I've tried by manually editing the marker shortcode class and it's working but only for image tags, not for svg only markers (it may need a fix, but since i'm using only images, it's not bothering me).

[bozdoz]

There is a demo of this in the Shortcode helper, so I believe it is working correctly.

Let me know if I'm misunderstanding this.