fix busybox image to 1.28 (issues with nslookup).

Changes where done with these commands:

reprec 'image: busybox(?!:)' 'image: busybox:1.28' */docs */examples
reprec -- '--image=busybox(?!:)' '--image=busybox:1.28' */docs */examples

Related issues:

 https://github.com/docker-library/busybox/issues/48
 https://github.com/kubernetes/kubernetes/issues/66924

content/en/examples/application/job/cronjob.yaml

@@ -10,7 +10,7 @@ spec:
         spec:
           containers:
           - name: hello
-            image: busybox
+            image: busybox:1.28
             imagePullPolicy: IfNotPresent
             command:
             - /bin/sh

content/en/examples/application/job/job-tmpl.yaml

@@ -13,6 +13,6 @@ spec:
     spec:
       containers:
       - name: c
-        image: busybox
+        image: busybox:1.28
         command: ["sh", "-c", "echo Processing item $ITEM && sleep 5"]
       restartPolicy: Never