Fix Thread leakage when scoring or testing submissions

It is discouraged to do anything directly within the
Tubesock hijack block. We might only use the callbacks
(onopen, onmessage, onclose, onerror). Otherwise,
Tubesock might not close all Threads correctly and
will keep them awake every five seconds.

Gemfile

@@ -42,7 +42,7 @@ gem 'sass-rails'
 gem 'slim-rails'
 gem 'sorcery' # Causes a deprecation warning in Rails 6.0+, see: https://github.com/Sorcery/sorcery/pull/255
 gem 'telegraf'
-gem 'tubesock', github: 'gosukiwi/tubesock', branch: 'patch-1' # Switch to a fork which is compatible with Rails 5
+gem 'tubesock'
 gem 'turbolinks'
 gem 'webpacker'
 gem 'whenever', require: false