pep8 fixes

vcr/persist.py

@@ -1,9 +1,11 @@
 from .persisters.filesystem import FilesystemPersister
 
+
 def load_cassette(cassette_path, serializer):
     with open(cassette_path) as f:
         return serializer.deserialize(f.read())
 
+
 def save_cassette(cassette_path, cassette_dict, serializer):
     data = serializer.serialize(cassette_dict)
     FilesystemPersister.write(cassette_path, data)