docs(kubectx): add quoting to array keys (#12216)

plugins/kubectx/README.md

@@ -17,9 +17,9 @@ One can rename default context name for better readability.
 
 _Example_. Add to **.zshrc**:
 ```
-kubectx_mapping[minikube]="mini"
-kubectx_mapping[context_name_from_kubeconfig]="$emoji[wolf_face]"
-kubectx_mapping[production_cluster]="%{$fg[yellow]%}prod!%{$reset_color%}"
+kubectx_mapping["minikube"]="mini"
+kubectx_mapping["context_name_from_kubeconfig"]="$emoji[wolf_face]"
+kubectx_mapping["production_cluster"]="%{$fg[yellow]%}prod!%{$reset_color%}"
 ```
 
 ![staging](stage.png)