Adding Facter gem to bundler config

This prevents the following error:
-----
RAILS_ENV=production bundle exec rake db:migrate
rake aborted!
cannot load such file -- facter
/usr/src/foreman/lib/tasks/reset_permissions.rake:1:in `<top (required)>'
/usr/src/foreman/Rakefile:7:in `<top (required)>'
(See full trace by running task with --trace)