Fix formatting of yum repo. (#8382)

First, fix https:// address.

Secondly, previous formatting would display on the page as one line
altogether, which couldn't be pasted into a terminal correctly.

content/en/docs/setup/independent/install-kubeadm.md

@@ -164,11 +164,11 @@ apt-get update
 apt-get install -y kubelet kubeadm kubectl
 {{< /tab >}}
 {{% tab name="CentOS, RHEL or Fedora" %}}
-``
+```
 cat <<EOF > /etc/yum.repos.d/kubernetes.repo
 [kubernetes]
 name=Kubernetes
-baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-\
+baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
 enabled=1
 gpgcheck=1
 repo_gpgcheck=1