Replace redirect links of install kubectl

/docs/tasks/tools/install-kubectl/ is redirected to
/docs/tasks/tools/
This commit replace the redirect links for installing kubectl
with direct links.

content/en/docs/setup/production-environment/tools/kops.md

@@ -23,7 +23,7 @@ kops is an automated provisioning system:
 ## {{% heading "prerequisites" %}}
 
 
-* You must have [kubectl](/docs/tasks/tools/install-kubectl/) installed.
+* You must have [kubectl](/docs/tasks/tools/) installed.
 
 * You must [install](https://github.com/kubernetes/kops#installing) `kops` on a 64-bit (AMD64 and Intel 64) device architecture.
 

content/en/docs/setup/production-environment/tools/kubeadm/install-kubeadm.md

@@ -160,7 +160,7 @@ kubelet and the control plane is supported, but the kubelet version may never ex
 server version. For example, the kubelet running 1.7.0 should be fully compatible with a 1.8.0 API server,
 but not vice versa.
 
-For information about installing `kubectl`, see [Install and set up kubectl](/docs/tasks/tools/install-kubectl/).
+For information about installing `kubectl`, see [Install and set up kubectl](/docs/tasks/tools/).
 
 {{< warning >}}
 These instructions exclude all Kubernetes packages from any system upgrades.