Fix serve_hostname image (#15416)

Signed-off-by: ialidzhikov <i.alidjikov@gmail.com>

content/en/docs/tasks/administer-cluster/namespaces.md

@@ -258,7 +258,7 @@ At this point, all requests we make to the Kubernetes cluster from the command l
 Let's create some contents.
 
 ```shell
-kubectl run snowflake --image=kubernetes/serve_hostname --replicas=2
+kubectl run snowflake --image=k8s.gcr.io/serve_hostname --replicas=2
 ```
 We have just created a deployment whose replica size is 2 that is running the pod called `snowflake` with a basic container that just serves the hostname.
 Note that `kubectl run` creates deployments only on Kubernetes cluster >= v1.2. If you are running older versions, it creates replication controllers instead.
@@ -298,7 +298,7 @@ kubectl get pods
 Production likes to run cattle, so let's create some cattle pods.
 
 ```shell
-kubectl run cattle --image=kubernetes/serve_hostname --replicas=5
+kubectl run cattle --image=k8s.gcr.io/serve_hostname --replicas=5
 
 kubectl get deployment
 ```