Clarify that 13.1.X is OK for csrf changes

The global_csrf_token FF was removed in 13.2.0

doc/update/README.md

@@ -263,9 +263,9 @@ with the older Rails version - which could cause non-GET requests to
 fail for [multi-node GitLab installations](https://docs.gitlab.com/omnibus/update/#multi-node--ha-deployment).
 
 So, if you are using multiple Rails servers and specifically upgrading from 13.0,
-all servers must first be upgraded to 13.1.0 before upgrading to later versions:
+all servers must first be upgraded to 13.1.X before upgrading to 13.2.0 or later:
 
-1. Ensure all GitLab web nodes are on GitLab 13.1.0.
+1. Ensure all GitLab web nodes are on GitLab 13.1.X.
 1. Optionally, enable the `global_csrf_token` feature flag to enable new
    method of CSRF token generation: