Allow to delete puzzles

app/models/contest.rb

@@ -1,4 +1,4 @@
 class Contest < ApplicationRecord
-  belongs_to :user, dependent: :destroy
-  has_many :puzzles
+  belongs_to :user
+  has_many :puzzles, dependent: :destroy
 end

app/models/puzzle.rb

@@ -1,5 +1,5 @@
 class Puzzle < ApplicationRecord
-  belongs_to :contest, dependent: :destroy
+  belongs_to :contest
   has_one_attached :image
   validates :name, presence: true
 end