debug-transform is broken with Python 3.9

The getchildren() method for xml.etree.ElementTree.Element was deprecated in Python 3.2 has been removed as of the Python 3.9.  This should be replaced by iter(x) or list(x) instead of x.getchildren().

This shows up in maltego/runner.py in console_writer.

https://docs.python.org/3/whatsnew/3.9.html#deprecated