Fixes asset host for development

config/environments/development.rb

@@ -16,6 +16,7 @@ Rails.application.configure do
   # Don't care if the mailer can't send.
   config.action_mailer.raise_delivery_errors = false
   config.action_mailer.default_url_options = { host: 'localhost', port: 3000 }
+  config.action_mailer.asset_host = "http://localhost:3000"
 
   # Deliver emails to a development mailbox at /letter_opener
   config.action_mailer.delivery_method = :letter_opener