rails: fix #to_s(:human_size) deprecation warnings.

Fix this deprecation warning:

  DEPRECATION WARNING: Integer#to_s(:human_size) is deprecated. Please use Integer#to_formatted_s(:human_size) instead.

app/models/post_flag.rb

@@ -102,7 +102,7 @@ class PostFlag < ApplicationRecord
 
     flag = post.flags.in_cooldown.last
     if !is_deletion && flag.present?
-      errors.add(:post, "cannot be flagged more than once every #{Danbooru.config.moderation_period.inspect} (last flagged: #{flag.created_at.to_s(:long)})")
+      errors.add(:post, "cannot be flagged more than once every #{Danbooru.config.moderation_period.inspect} (last flagged: #{flag.created_at.to_formatted_s(:long)})")
     end
   end
 

app/views/uploads/index.html.erb

@@ -21,7 +21,7 @@
         <% if upload.post.present? %>
           <span class="info">
             <strong>Size</strong>
-            <%= link_to "#{upload.post.file_size.to_s(:human_size, precision: 4)} #{upload.post.file_ext}", upload.post.file_url %>
+            <%= link_to "#{upload.post.file_size.to_formatted_s(:human_size, precision: 4)} #{upload.post.file_ext}", upload.post.file_url %>
             (<%= upload.post.image_width %>x<%= upload.post.image_height %>)
           </span>
         <% end %>