Use where.not instead of where(NOT IN)

This way we simplify the code a bit and reduce our usage of raw SQL.

app/controllers/proposals_controller.rb

@@ -158,7 +158,7 @@ class ProposalsController < ApplicationController
                               .sort_by_confidence_score.limit(Setting["featured_proposals_number"])
         if @featured_proposals.present?
           set_featured_proposal_votes(@featured_proposals)
-          @resources = @resources.where("proposals.id NOT IN (?)", @featured_proposals.map(&:id))
+          @resources = @resources.where.not(id: @featured_proposals)
         end
       end
     end