Wrong check for ElementTree classes

I get this:

```pytb
TypeError: <xml.etree.ElementTree.ElementTree object at 0x7fcb00395e80> is of type <class 'xml.etree.ElementTree.ElementTree'>.
           This object only can displays objects of type str, bytes, lxml.etree._ElementTree, or lxml.etree._Element.
```

It should also support stdlib etree objects