Update rails, gems, use MathJax over CDN

config/environments/production.rb

@@ -14,10 +14,9 @@ Rails.application.configure do
   config.consider_all_requests_local       = false
   config.action_controller.perform_caching = true
 
-  # Attempt to read encrypted secrets from `config/secrets.yml.enc`.
-  # Requires an encryption key in `ENV["RAILS_MASTER_KEY"]` or
-  # `config/secrets.yml.key`.
-  config.read_encrypted_secrets = true
+  # Ensures that a master key has been made available in either ENV["RAILS_MASTER_KEY"]
+  # or in config/master.key. This key is used to decrypt credentials (and other encrypted files).
+  config.require_master_key = true
 
   # Disable serving static files from the `/public` folder by default since
   # Apache or NGINX already handles this.
@@ -30,8 +29,6 @@ Rails.application.configure do
   # Do not fallback to assets pipeline if a precompiled asset is missed.
   config.assets.compile = false
 
-  config.assets.digest = true
-
   # `config.assets.precompile` and `config.assets.version` have moved to config/initializers/assets.rb
 
   # Enable serving of images, stylesheets, and JavaScripts from an asset server.
@@ -41,6 +38,9 @@ Rails.application.configure do
   # config.action_dispatch.x_sendfile_header = 'X-Sendfile' # for Apache
   # config.action_dispatch.x_sendfile_header = 'X-Accel-Redirect' # for NGINX
 
+  # Store uploaded files on the local file system (see config/storage.yml for options)
+  config.active_storage.service = :local
+
   # Mount Action Cable outside main process or domain
   # config.action_cable.mount_path = nil
   # config.action_cable.url = 'wss://example.com/cable'
@@ -62,6 +62,7 @@ Rails.application.configure do
   # Use a real queuing backend for Active Job (and separate queues per environment)
   # config.active_job.queue_adapter     = :resque
   # config.active_job.queue_name_prefix = "projekteuler_#{Rails.env}"
+
   config.action_mailer.perform_caching = false
 
   # Ignore bad email addresses and do not raise email delivery errors.