Fixed forgotten unicorn to puma in a comment.

config/gitlab.yml.example

@@ -19,7 +19,7 @@ production: &base
     port: 80
     https: false
     # Uncomment and customize to run in non-root path
-    # Note that ENV['RAILS_RELATIVE_URL_ROOT'] in config/unicorn.rb may need to be changed
+    # Note that ENV['RAILS_RELATIVE_URL_ROOT'] in config/puma.rb may need to be changed
     # relative_url_root: /gitlab
     # Uncomment and customize if you can't use the default user to run GitLab (default: 'git')