Update important-changes.mdx (#687)

Added missing "audience=myapp \" param to k8s auth role definition.

Author: schavis

content/vault/v1.20.x/content/docs/updates/important-changes.mdx

@@ -105,6 +105,7 @@ vault write auth/kubernetes/role/demo \
     bound_service_account_names=myapp \
     bound_service_account_namespaces=default \
     policies=default \
+    audience=myapp \
     ttl=1h
 ```