Fix invalid task name migrate_global_keys

doc/update/5.4-to-6.0.md

@@ -36,7 +36,7 @@ sudo -u git -H bundle install --without development test mysql --deployment
 sudo -u git -H bundle exec rake db:migrate RAILS_ENV=production
 sudo -u git -H bundle exec rake migrate_groups RAILS_ENV=production
 sudo -u git -H bundle exec rake migrate_global_projects RAILS_ENV=production
-sudo -u git -H bundle exec rake migrate_global_keys RAILS_ENV=production
+sudo -u git -H bundle exec rake migrate_keys RAILS_ENV=production
 ```