もしかして実質的な差は1行だけ？
diff --git a/Gemfile b/Gemfile
index 6ee884a1..95c74eef 100644
--- a/Gemfile
+++ b/Gemfile
@@ -18,6 +18,7 @@ gem 'aws-sdk', '~> 2.9'
gem 'paperclip', '~> 5.1'
gem 'paperclip-av-transcoder', '~> 0.6'
+gem 'active_model_serializers', '~> 0.10'
gem 'addressable', '~> 2.5'
gem 'bootsnap'
gem 'browser'