This commit improves to display the default value of --kube-version in
help message of `helm template` command.
```
--kube-version string kubernetes version used as Capabilities.KubeVersion.Major/Minor (default "1.9")
```
f.StringVar(&t.namespace,"namespace","","namespace to install the release into")
f.StringArrayVar(&t.values,"set",[]string{},"set values on the command line (can specify multiple or separate values with commas: key1=val1,key2=val2)")
f.StringVar(&t.nameTemplate,"name-template","","specify template used to name the release")
f.StringVar(&t.kubeVersion,"kube-version","","override the Kubernetes version used as Capabilities.KubeVersion.Major/Minor (e.g. 1.7)")
f.StringVar(&t.kubeVersion,"kube-version",defaultKubeVersion,"kubernetes version used as Capabilities.KubeVersion.Major/Minor")
f.StringVar(&t.outputDir,"output-dir","","writes the executed templates to files in output-dir instead of stdout")