Fix generated Gemfile missing gems on jruby

[deivid-rodriguez]

Summary

I noticed that when generating a Rails application on jruby, development and test gems are never included. On Linux in particular, that causes the generated application to fail in development because the file_watcher is configured to depend on listen, but the listen gem is not included.

This PR should fix that.

[rails-bot]

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[y-yagi]

Thanks!