Fixed a couple flake8 warnings.

django/core/cache/backends/filebased.py

@@ -152,7 +152,6 @@ class FileBasedCache(BaseCache):
         return filelist
 
 
-
 # For backwards compatibility
 class CacheClass(FileBasedCache):
     pass

tests/cache/tests.py

@@ -4,7 +4,6 @@
 # Uses whatever cache backend is set in the test settings file.
 from __future__ import unicode_literals
 
-import hashlib
 import os
 import pickle
 import random

tests/prefetch_related/tests.py

@@ -492,6 +492,7 @@ class CustomPrefetchTests(TestCase):
         self.assertEqual(lst2[0].houses_lst[0].rooms_lst[1], self.room1_2)
         self.assertEqual(len(lst2[1].houses_lst), 0)
 
+
 class DefaultManagerTests(TestCase):
 
     def setUp(self):