Use where.not instead of where(NOT IN)

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

lib/user_segments.rb

@@ -45,10 +45,9 @@ class UserSegments
 
   def self.not_supported_on_current_budget
     author_ids(
-      User.where(
-                  "id NOT IN (?)",
-                  Vote.select(:voter_id).where(votable: current_budget_investments).distinct
-                )
+      User.where.not(
+        id: Vote.select(:voter_id).where(votable: current_budget_investments).distinct
+      )
     )
   end