chore(deps): update dependency validates_timeliness to v8

Author: renovate[bot]

Gemfile

@@ -40,7 +40,7 @@ gem 'simple_form', '~> 5.1.0'
 gem 'slack-notifier', '~> 2.4.0'
 gem 'turbolinks', '~> 5.2.0'
 gem 'uglifier', '~> 4.2.0'
-gem 'validates_timeliness', '~> 7.0.0.beta2'
+gem 'validates_timeliness', '~> 8.0.0'
 gem 'webpacker', '~> 5.4.0'
 gem 'wicked_pdf'
 gem 'wkhtmltopdf-binary'