Addresses typo in (#192) @ clean up snippets

See (DarrenOfficial/dpaste#215)

dpaste/management/commands/cleanup_snippets.py

@@ -39,7 +39,7 @@ def handle(self, *args, **options):
                         timezone.now() - timedelta(seconds=config.EXPIRE_DEFAULT)
                     ),
                 )
-            deleteable_snippets = (expired_snippets | onetime_unviewed_snippets)
+            deleteable_snippets = (deleteable_snippets | onetime_unviewed_snippets)
 
         if len(deleteable_snippets) == 0:
             self.stdout.write(u"No snippets to delete.")