FIX: Missing `url` attribute for suggested topics

app/serializers/similar_topic_serializer.rb

@@ -1,7 +1,7 @@
 class SimilarTopicSerializer < ApplicationSerializer
 
   has_one :topic, serializer: TopicListItemSerializer, embed: :ids
-  attributes :id, :blurb, :created_at
+  attributes :id, :blurb, :created_at, :url
 
   def id
     object.topic.id
@@ -11,6 +11,10 @@ class SimilarTopicSerializer < ApplicationSerializer
     object.blurb
   end
 
+  def url
+    object.topic.url
+  end
+
   def created_at
     object.topic.created_at
   end