Display correct max subdomain length

openappstack/__main__.py

@@ -132,7 +132,8 @@ def main():  # pylint: disable=too-many-statements,too-many-branches,too-many-lo
     droplet_creation_group.add_argument(
         '--truncate-subdomain',
         action='store_true',
-        help=('Truncate subdomain so subdomain and domain are shorter than 56 characters.'))
+        help=('Truncate subdomain so subdomain and domain are shorter than '
+              '{} characters.'.format(MAX_DOMAIN_LENGTH)))
 
     droplet_creation_group.add_argument(
         '--acme-staging',