Small fixes to the installation guide and check task

lib/tasks/gitlab/check.rake

@@ -730,7 +730,7 @@ namespace :gitlab do
         puts "no".red
         try_fixing_it(
           "sudo chmod -R ug+rwX,o-rwx #{repo_base_path}",
-          "sudo chmod -R u-s #{repo_base_path}",
+          "sudo chmod -R ug-s #{repo_base_path}",
           "find #{repo_base_path} -type d -print0 | sudo xargs -0 chmod g+s"
         )
         for_more_information(