[format.python] initial formatting of the python code

This patch was generated by black [1]::

    make format.python

[1] https://github.com/psf/black

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

tests/unit/engines/test_xpath.py

@@ -6,7 +6,6 @@ from tests import SearxTestCase
 
 
 class TestXpathEngine(SearxTestCase):
-
     def test_request(self):
         xpath.search_url = 'https://url.com/{query}'
         xpath.categories = []