Force select2-rails to 3.2.1 [Fixes #3039]

select2-rails 3.2.2 breaks all capybara helpers in Spree that depends on
the label tag for attribute. e.g.

    <%= label_tag :add_variant_id, Spree.t(:name_or_sku) %>

    Instead of:

    <label for="s2id_add_variant_id">some text</label>

    will generate:

    <label for="s2id_autogen1">some text</label>

see https://github.com/ivaynberg/select2/commit/519070b11da9347cf1542d26fc59a83b0c3fd934

wtf select2 ..

Fix request specs