optimize image upload queries

Author: drusepth

app/views/content/cards/_in_universe_content_list.html.erb

@@ -5,7 +5,7 @@
 %>
 <div class="card hoverable">
   <div class="card-image">
-    <% images = ImageUpload.where(content_type: content_type_name, content_id: content_list.map(&:id)) %>
+    <% images = ImageUpload.where(content_type: content_type_name, content_id: content_list.pluck(:id)) %>
     <% if images.any? && rand(3) < 2 %>
       <%= image_tag images.sample.src(:large), class: 'activator', style: 'height: 265px' %>
     <% else %>