Fix "processing" page for private asciicasts

app/serializers/asciicast_serializer.rb

@@ -5,6 +5,10 @@ class AsciicastSerializer < ActiveModel::Serializer
   attribute :terminal_columns, key: :width
   attribute :terminal_lines, key: :height
 
+  def id
+    object.to_param
+  end
+
   def private?
     object.private?
   end

spec/serializers/asciicast_serializer_spec.rb

@@ -9,7 +9,7 @@ describe AsciicastSerializer do
     subject { JSON.parse(serializer.to_json) }
 
     it 'includes id' do
-      expect(subject['id']).to eq(asciicast.id)
+      expect(subject['id']).to eq(asciicast.to_param)
     end
 
     it 'includes duration' do