Update Movie.default_list_order scope with safe SQL

[lortza]

I am seeing this warning in our spec output and we'll need to address it before upgrading to rails 6 (or ideally right away).

DEPRECATION WARNING: Dangerous query method (method whose arguments are used as raw SQL) called with non-attribute argument(s): "CAST(listings.created_at as DATE) desc, listings.priority desc". Non-attribute arguments will be disallowed in Rails 6.0. This method should not be called with user-provided values, such as request parameters or model attributes. Known-safe values can be passed by wrapping them in Arel.sql(). (called from block in class:Movie at /app/models/movie.rb:29)

# /app/models/movie.rb:29

 scope :default_list_order, -> (list) do
    list.movies.order('CAST(listings.created_at as DATE) desc, listings.priority desc')
  end