Fixed a zsh bug

Using double quotes causes the code to be evaluated too early and ends up not working if you don't have kubectl installed.

Author: jjinux

content/en/docs/reference/kubectl/cheatsheet.md

@@ -37,7 +37,7 @@ complete -o default -F __start_kubectl k
 
 ```bash
 source <(kubectl completion zsh)  # setup autocomplete in zsh into the current shell
-echo "[[ $commands[kubectl] ]] && source <(kubectl completion zsh)" >> ~/.zshrc # add autocomplete permanently to your zsh shell
+echo '[[ $commands[kubectl] ]] && source <(kubectl completion zsh)' >> ~/.zshrc # add autocomplete permanently to your zsh shell
 ```
 ### A Note on --all-namespaces