Leaderboard answers only from current week (#34)

* Update weekly leaderboard to only include answers from puzzles form that week

* Rubocop fixes

* Add joins

Author: FionaDL

app/jobs/weekly_leaderboard_job.rb

@@ -7,7 +7,8 @@ def perform
     end_time = Time.now.utc.end_of_week.end_of_day # Sunday at 23:59 UTC
 
     leaderboard_data = Answer
-      .where(created_at: start_time..end_time, is_correct: true)
+      .joins(:puzzle)
+      .where(created_at: start_time..end_time, is_correct: true, puzzles: { sent_at: start_time..end_time })
       .group(:server_id, :user_id)
       .order(Arel.sql("COUNT(*) DESC"))
       .count