Add newline to align with blocks_by

`blocks_on.html.erb` is almost identical to `block_by.html.erb`. Add a newline to align with the other file (makes it easier to see the more subtle important difference)

app/views/user_blocks/blocks_on.html.erb

@@ -2,6 +2,7 @@
 <% content_for :heading do %>
   <h1><%= t(".heading_html", :name => link_to(@user.display_name, user_path(@user))) %></h1>
 <% end %>
+
 <% unless @user_blocks.empty? %>
 <%= render :partial => "blocks", :locals => { :show_revoke_link => can?(:revoke, UserBlock), :show_user_name => false, :show_creator_name => true } %>
 <% else %>