Fix Rubocop offenses

spec/factories/code_ocean/file.rb

@@ -6,15 +6,15 @@ module CodeOcean
   FactoryBot.define do
     factory :file, class: 'CodeOcean::File' do
       content { '' }
-      association :context, factory: :submission
-      association :file_type, factory: :dot_rb
+      context factory: :submission
+      file_type factory: :dot_rb
       hidden { false }
       name { SecureRandom.hex }
       read_only { false }
       role { 'main_file' }
 
       trait(:image) do
-        association :file_type, factory: :dot_png
+        file_type factory: :dot_png
         name { 'poster' }
         native_file { Rack::Test::UploadedFile.new(Rails.root.join('db/seeds/audio_video/poster.png'), 'image/png') }
       end
@@ -22,8 +22,8 @@ module CodeOcean
 
     factory :test_file, class: 'CodeOcean::File' do
       content { '' }
-      association :context, factory: :dummy
-      association :file_type, factory: :dot_rb
+      context factory: :dummy
+      file_type factory: :dot_rb
       hidden { true }
       name { SecureRandom.hex }
       read_only { true }