Added some missing whitespace around arithmetic operators

tests/migrations/test_writer.py

@@ -103,7 +103,7 @@ class WriterTests(TestCase):
             )
         )
         self.assertSerializedResultEqual(
-            ((x, x*x) for x in range(3)),
+            ((x, x * x) for x in range(3)),
             (
                 "((0, 0), (1, 1), (2, 4))",
                 set(),