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/docs/tutorials/services/source-ip.md

@@ -119,7 +119,7 @@ clusterip    ClusterIP   10.0.170.92   <none>        80/TCP    51s
 And hitting the `ClusterIP` from a pod in the same cluster:
 
 ```shell
-kubectl run busybox -it --image=busybox --restart=Never --rm
+kubectl run busybox -it --image=busybox:1.28 --restart=Never --rm
 ```
 The output is similar to this:
 ```