Remove GitLab 4 version reference in docs

Remove version 4 reference from Namespaces doc

doc/raketasks/features.md

@@ -10,7 +10,8 @@ This Rake task enables [namespaces](../user/group/index.md#namespaces) for proje
 
 ## Enable usernames and namespaces for user projects
 
-This command enables the namespaces feature introduced in GitLab 4.0. It moves every project in its namespace folder.
+This command enables the namespaces feature. It moves every project in its
+namespace folder.
 
 The **repository location changes as part of this task**, so you must **update all your Git URLs** to
 point to the new location.