fix older content of 1.17.x

Author: soolaugust

content/en/docs/tasks/administer-cluster/kubeadm/kubeadm-upgrade.md

@@ -50,18 +50,18 @@ The upgrade workflow at high level is the following:
 
 ## Determine which version to upgrade to
 
-1.  Find the latest stable 1.17 version:
+1.  Find the latest stable 1.18 version:
 
     {{< tabs name="k8s_install_versions" >}}
     {{% tab name="Ubuntu, Debian or HypriotOS" %}}
     apt update
     apt-cache madison kubeadm
-    # find the latest 1.17 version in the list
+    # find the latest 1.18 version in the list
     # it should look like 1.18.x-00, where x is the latest patch
     {{% /tab %}}
     {{% tab name="CentOS, RHEL or Fedora" %}}
     yum list --showduplicates kubeadm --disableexcludes=kubernetes
-    # find the latest 1.17 version in the list
+    # find the latest 1.18 version in the list
     # it should look like 1.18.x-0, where x is the latest patch
     {{% /tab %}}
     {{< /tabs >}}