Update rubocop and friends

Updates the following dependencies:
- rubocop to 0.81.x
- rubocop-rspec to 1.38.x

The rubocop-performance dependency is kept at 1.5.x.

These are the last minor versions that support Ruby 2.3.

cucumber-rails.gemspec

@@ -34,9 +34,9 @@ Gem::Specification.new do |s|
   s.add_development_dependency('bundler', '>= 1.17')
   s.add_development_dependency('rake', '>= 12.0')
   s.add_development_dependency('rspec', '~> 3.6')
-  s.add_development_dependency('rubocop', '~> 0.78.0')
+  s.add_development_dependency('rubocop', '~> 0.81.0')
   s.add_development_dependency('rubocop-performance', '~> 1.5.0')
-  s.add_development_dependency('rubocop-rspec', '~> 1.37.0')
+  s.add_development_dependency('rubocop-rspec', '~> 1.38.0')
   s.add_development_dependency('sqlite3', '~> 1.3')
 
   # For Documentation: