update examples/cluster-dns to v1

examples/cluster-dns/dns-backend-rc.yaml

-apiVersion: v1beta3
+apiVersion: v1
 kind: ReplicationController
 metadata:
   name: dns-backend
@@ -19,4 +19,3 @@ spec:
           ports:
             - name: backend-port
               containerPort: 8000
-              protocol: tcp

examples/cluster-dns/dns-backend-service.yaml

 kind: Service
-apiVersion: v1beta3
+apiVersion: v1
 metadata:
   name: dns-backend
 spec:

examples/cluster-dns/dns-frontend-pod.yaml

-apiVersion: v1beta3
+apiVersion: v1
 kind: Pod
 metadata:
   name: dns-frontend

examples/cluster-dns/namespace-dev.yaml

-apiVersion: v1beta3
+apiVersion: v1
 kind: Namespace
 metadata:
   name: "development"

examples/cluster-dns/namespace-prod.yaml

-apiVersion: v1beta3
+apiVersion: v1
 kind: Namespace
 metadata:
   name: "production"