Add quotes to jsonpath in elasticsearch tutorial

[mynameiswhm]

Some shells (zsh, in my case) use curly braces for pattern expansion differently than sh/bash, so provided command fails:

$ kubectl exec -it $(kubectl get pods --all-namespaces -l app=kubedb -o jsonpath={.items[0].metadata.name}) -n kube-system sh

zsh: no matches found: jsonpath={.items[0].metadata.name}
error: expected 'exec POD_NAME COMMAND [ARG1] [ARG2] ... [ARGN]'.
POD_NAME and COMMAND are required arguments for the exec command
See 'kubectl exec -h' for help and examples.

I've added quotes to aviod that.

[tamalsaha]

Thanks @mynameiswhm !