update slug "artists" -> "barbarella"

want to use/give Barbarella name recognition

config.toml

 [[menu.pages]]
   name = "Artists"
   weight = -90
-  identifier = "artists"
-  url = "/artists/"
+  identifier = "barbarella"
+  url = "/barbarella/"
 
 [outputs]
   home = ["HTML"]

content/artists.md

 ---
 title: Artists
 language: en
-slug: artists
+slug: barbarella
 ---
 
 <div class="cognito">