Update this octal literal to be Python3 compatible.

The `"0" 1*digits` syntax is gone in Python 3. This syntax replaced it.
It was ported into Python 2 at 2.6[1].

[1]: https://docs.python.org/2/whatsnew/2.6.html

letsencrypt/storage.py

@@ -694,7 +694,7 @@ class RenewableCert(object):  # pylint: disable=too-many-instance-attributes
         for i in (cli_config.renewal_configs_dir, cli_config.archive_dir,
                   cli_config.live_dir):
             if not os.path.exists(i):
-                os.makedirs(i, 0700)
+                os.makedirs(i, 0o700)
                 logger.debug("Creating directory %s.", i)
         config_file, config_filename = le_util.unique_lineage_name(
             cli_config.renewal_configs_dir, lineagename)