Fix test_pow for Python 3.8+

Author: shadchin

tests/test_future/test_builtins.py

@@ -1304,7 +1304,8 @@ def test_pow(self):
         self.assertAlmostEqual(pow(-1, 1/3), 0.5 + 0.8660254037844386j)
 
         # Raises TypeError in Python < v3.5, ValueError in v3.5:
-        self.assertRaises((TypeError, ValueError), pow, -1, -2, 3)
+        if sys.version_info < (3, 8):
+            self.assertRaises((TypeError, ValueError), pow, -1, -2, 3)
         self.assertRaises(ValueError, pow, 1, 2, 0)
 
         self.assertRaises(TypeError, pow)