Change the default CarrierWave root path for tests

This more closely resembles the development and production paths in that
paths contain `public/uploads`, rather than `uploads/uploads` as they
did before.

spec/support/carrierwave.rb

-CarrierWave.root = File.expand_path('tmp/tests/uploads', Rails.root)
+CarrierWave.root = File.expand_path('tmp/tests/public', Rails.root)
 
 RSpec.configure do |config|
   config.after(:each) do