<% content.attributors.each do |user| %>
  <div class="user <% if user.verified_professor? %> verified <% end %>">
    <%= link_to user.display_name, user_path(user) %><%= ", " unless content.owners.count == content.collaborators.count %>
  </div>
<% end %>

<% content.attributors.each do |user| %>
  <div class="user <% if user.verified_professor? %> verified <% end %>">
    <%= link_to user.display_name, user_path(user) %><%= ", " unless content.attributors.last == user %>
  </div>
<% end %>

Correct comma seperation when showing authors.
Correct comma seperation when showing authors.
