Update kubelet-config-file.md

Updated the link from v1alpha1 to v1beta1

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 (v1beta1)](https://github.com/kubernetes/kubernetes/blob/master/pkg/kubelet/apis/kubeletconfig/v1beta1/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.