Outdated instructions on theming: env.config.use_ls_colors

Hi all!

I found this on 

https://www.nushell.sh/book/coloring_and_theming.html#theming

````
$env.config.use_ls_colors: true
````

It should be 

````
$env.config.ls.use_ls_colors: true
````

Best,
Vatsa