devel/rubygem-rdoc63: restore version 6.3.3

Version 6.4 shows segfaults if used with gitlab-ce:
su -l git -c "cd /usr/local/www/gitlab-ce && RAILS_ENV=production NODE_ENV=production USE_DB=false SKIP_STORAGE_VALIDATION=true NODE_OPTIONS='--max_old_space_size=3584' bundle exec rake gitlab:assets:compile"

rake aborted!
Psych::BadAlias: Unknown alias: base
/usr/local/www/gitlab-ce/config/initializers/1_settings.rb:8:in `<top (required)>'
/usr/local/www/gitlab-ce/config/environment.rb:7:in `<top (required)>'
/usr/local/www/gitlab-ce/lib/gitlab/task_helpers.rb:18:in `invoke_and_time_task'
/usr/local/www/gitlab-ce/lib/tasks/gitlab/assets.rake:61:in `each'
/usr/local/www/gitlab-ce/lib/tasks/gitlab/assets.rake:61:in `block (3 levels) in <top (required)>'
/usr/local/bin/bundle:23:in `load'
/usr/local/bin/bundle:23:in `<main>'
Tasks: TOP => gettext:po_to_json => environment