IE11, d&d starting from an SVG element (like path) fails + toLowerCase call on undefined error

On IE11, for unknown reasons, it seems we are unable to get the tagname:

```javascript
shouldCancelStart: function(e) {
// Cancel sorting if the event target is an `input`, `textarea`, `select` or `option`
const disabledElements = ['input', 'textarea', 'select', 'option', 'button'];

if (disabledElements.indexOf(e.target.tagName.toLowerCase()) !== -1) {
return true; // Return true to cancel sorting
}
},
```

shouldCancelStart calls toLowerCase on null/undefined on IE11

https://github.com/clauderic/react-sortable-hoc/blob/e599da7fefa5550f9a1d65cad302e5c77ea6ac7b/src/SortableContainer/index.js#L51

We got in production this error: `#40 TypeError: Impossible d’obtenir la propriété « toLowerCase » d’une référence null ou non définie` which means tagName is null or undefined

Not sure exactly when it happens, but it does.