I commented on the OP's article, but do this for the pk:

    create_table(:users, id: :uuid) do |t|
      t.string 'name'
    end

And to make sure the extension is enabled, (in your migrations) do:

    enable_extension 'uuid-ossp'

For now, make sure to use SQL schema dumping. I don't think Ruby schema files will work (as I haven't written a test for it yet).

EDIT: I forgot to mention, you can enable hstore by using "enable_extension('hstore')"