Merge pull request #20291 from sftim/20200413_fix_kubeadm_yum_repo_configuration_command

Fix incorrect here document in https://k8s.io/docs/setup/production-environment/tools/kubeadm/

Author: k8s-ci-robot

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

@@ -194,7 +194,7 @@ sudo apt-mark hold kubelet kubeadm kubectl
 cat <<EOF > /etc/yum.repos.d/kubernetes.repo
 [kubernetes]
 name=Kubernetes
-baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-$basearch
+baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-\$basearch
 enabled=1
 gpgcheck=1
 repo_gpgcheck=1