Point the KubeletConfig doc to the release-1.9 code base

The version will be updated to v1beta1 with the official 1.10 release.

docs/tasks/administer-cluster/kubelet-config-file.md

@@ -27,7 +27,7 @@ providing parameters via a config file, which simplifies node deployment.
 
 The subset of the Kubelet's configuration that can be configured via a file
 is defined by the `KubeletConfiguration` struct
-[here (v1alpha1)](https://github.com/kubernetes/kubernetes/blob/master/pkg/kubelet/apis/kubeletconfig/v1alpha1/types.go).
+[here (v1alpha1)](https://github.com/kubernetes/kubernetes/blob/release-1.9/pkg/kubelet/apis/kubeletconfig/v1alpha1/types.go).
 The configuration file must be a JSON or YAML representation of the parameters
 in this struct. Note that this structure, and thus the config file API,
 is still considered alpha and is not subject to stability guarantees.