Currently, there is only one gem for all platform, and that gem
blindly includes a bunch of jars, which currently includes jruby.jar
(all 8.3 MB's): https://github.com/mongodb/mongo-ruby-driver/blob/master/bson.gemspec#L17

It would be much nicer if there was platform specific gems: 1 for
jruby, and one for everything else, without the jars. Thanks!