Apply suggestions from code review

Co-authored-by: Tianon Gravi <admwiggin@gmail.com>

prepare-vms/lib/commands.sh

@@ -267,7 +267,7 @@ _cmd_docker() {
 
     # Add registry mirror configuration.
     if ! [ -f /etc/docker/daemon.json ]; then
-    	sudo mkdir -p /etc/docker
+        sudo mkdir -p /etc/docker
         echo '{\"registry-mirrors\": [\"https://mirror.gcr.io\"]}' | sudo tee /etc/docker/daemon.json
         sudo systemctl restart docker
     fi