Make Checkystyle ElementTree.

def finished(self, filename):
        """Make Checkystyle ElementTree."""
        if len(self.errors) < 1:
            return

        element = ET.SubElement(self.checkstyle_element, 'file', name=filename)
        for error in self.errors:
            message = error.code + ' ' + error.text
            prefix = error.code.strip()[0]
            ET.SubElement(element, 'error', {
                'severity': CHECKSTYLE_SERVERITY.get(prefix, 'info'),
                'line': str(error.line_number),
                'column': str(error.column_number),
                'message': message,
                'source': CHECKSTYLE_SOURCE.get(prefix, 'undefined code'),
            }
            )