fixes kubeadm upgrade index

Author: mhausenblas

_data/tasks.yml

@@ -134,7 +134,7 @@ toc:
   - docs/tasks/administer-cluster/cluster-management.md
   - docs/tasks/administer-cluster/upgrade-1-6.md
   - docs/tasks/administer-cluster/kubeadm-upgrade-1-7.md
-  - docs/tasks/administer-cluster/kubeadm-upgrade-cmd.md
+  - docs/tasks/administer-cluster/kubeadm-upgrade-1-8.md
   - docs/tasks/administer-cluster/namespaces.md
   - docs/tasks/administer-cluster/namespaces-walkthrough.md
   - docs/tasks/administer-cluster/dns-horizontal-autoscaling.md