changed uprate to promote

changed word to better clarify actions used in kubernetes cluster

Author: tedleyem

content/en/docs/setup/production-environment/_index.md

@@ -9,7 +9,7 @@ no_list: true
 A production-quality Kubernetes cluster requires planning and preparation.
 If your Kubernetes cluster is to run critical workloads, it must be configured to be resilient.
 This page explains steps you can take to set up a production-ready cluster,
-or to upgrade an existing cluster for production use.
+or to promote an existing cluster for production use.
 If you're already familiar with production setup and want the links, skip to
 [What's next](#what-s-next).