Fix flannel revision for 1.16+

This version of flannel manifests include `cniVersion` that is
required for it to work properly with Kubernetes 1.16+.

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

@@ -376,7 +376,7 @@ Note that `flannel` works on `amd64`, `arm`, `arm64`, `ppc64le` and `s390x` unde
 Windows (`amd64`) is claimed as supported in v0.11.0 but the usage is undocumented.
 
 ```shell
-kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/32a765fd19ba45b387fdc5e3812c41fff47cfd55/Documentation/kube-flannel.yml
+kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/2140ac876ef134e0ed5af15c65e414cf26827915/Documentation/kube-flannel.yml
 ```
 
 For more information about `flannel`, see [the CoreOS flannel repository on GitHub