Add RSpec 4 compatibility (#17652)

* Remove outdated option

04078317ba

* Use the non-globally exposed RSpec syntax

https://github.com/rspec/rspec-core/pull/2803

* Use the non-globally exposed RSpec syntax, cont

https://github.com/rspec/rspec-core/pull/2803

* Comply to strict predicate matchers

See:
 - https://github.com/rspec/rspec-expectations/pull/1195
 - https://github.com/rspec/rspec-expectations/pull/1196
 - https://github.com/rspec/rspec-expectations/pull/1277

spec/integrity/coding_style_spec.rb

@@ -17,7 +17,7 @@ def grep_file(file, regex)
   lines.count > 0 ? file : nil
 end
 
-describe 'Coding style' do
+RSpec.describe 'Coding style' do
   describe 'Javascript' do
     it 'prevents this.get("foo") pattern' do
       js_files = list_js_files('app/assets/javascripts')