Resolve needless inheritence from object (Python 3)

docs/advanced.rst

@@ -71,7 +71,7 @@ Finally, register your class with VCR to use your new serializer.
 
     import vcr
 
-    class BogoSerializer(object):
+    class BogoSerializer:
         """
         Must implement serialize() and deserialize() methods
         """

tests/integration/test_register_persister.py

@@ -10,7 +10,7 @@ import vcr
 from vcr.persisters.filesystem import FilesystemPersister
 
 
-class CustomFilesystemPersister(object):
+class CustomFilesystemPersister:
     """Behaves just like default FilesystemPersister but adds .test extension
     to the cassette file"""