flake8 fix

test/test_persistent_dict.py

@@ -261,7 +261,7 @@ def test_write_once_persistent_dict_cache_collisions():
         key2 = PDictTestingKeyOrValue(2, hash_key=0)
         pdict[key1] = 1
 
-        # check lookup        
+        # check lookup
         with pytest.warns(UserWarning):
             with pytest.raises(NoSuchEntryError):
                 pdict[key2]