Fix a bug while setting the hostname for all machines

[gersonsosa]

Fixes the sed command that adds a line to the /etc/hosts to change the hostname and the fully qualified name file for each machine.

Discovered it because the output of this command is different

kubernetes-the-hard-way/docs/03-compute-resources.md

Lines 116 to 125 in a9cb5f7

	```bash
	while read IP FQDN HOST SUBNET; do
	ssh -n root@${IP} hostname --fqdn
	done < machines.txt
	```
	```text
	server.kubernetes.local
	node-0.kubernetes.local
	node-1.kubernetes.local