Fixed typo in gitlab.yml.example

Created by: mlitwiniuk

When installing gitlab on next host I've noticed a typo. So here's fix.

app/controllers/profiles_controller.rb

@@ -51,7 +51,9 @@ class ProfilesController < ApplicationController
   end
   def update_username
-    @user.update_attributes(username: params[:user][:username])
+    if Gitlab.config.gitlab.username_changing_enabled
+      @user.update_attributes(username: params[:user][:username])
+    end
     respond_to do |format|
       format.js