Use RuboCop RSpec 2.18

This commit makes this repo to use RuboCop RSpec 2.18 and suppress the following new offenses:

```consle
% bundle exec rake
(snip)

Offenses:

spec/project_spec.rb:22:9: C: [Correctable] RSpec/PredicateMatcher: Prefer using include? over include matcher.
        expect(description).not_to include("\n")
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
spec/rubocop/cop/rails/validation_spec.rb:11:7: C: [Correctable] RSpec/PredicateMatcher: Prefer using include? over include matcher.
      expect(offenses.first.message).to include(described_class::ALLOWLIST[number])
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

279 files inspected, 2 offenses detected, 2 offenses autocorrectable
````

Author: koic

Gemfile

@@ -11,7 +11,7 @@ gem 'rake'
 gem 'rspec'
 gem 'rubocop', github: 'rubocop/rubocop'
 gem 'rubocop-performance', '~> 1.15.0'
-gem 'rubocop-rspec', '~> 2.16.0'
+gem 'rubocop-rspec', '~> 2.18.0'
 gem 'simplecov'
 gem 'test-queue'
 gem 'yard', '~> 0.9'

spec/project_spec.rb

@@ -19,7 +19,7 @@
       cop_names.each do |name|
         description = config[name]['Description']
         expect(description.nil?).to be(false)
-        expect(description).not_to include("\n")
+        expect(description.include?("\n")).to be(false)
 
         start_with_subject = description.match(/\AThis cop (?<verb>.+?) .*/)
         suggestion = start_with_subject[:verb]&.capitalize if start_with_subject

spec/rubocop/cop/rails/validation_spec.rb

@@ -8,7 +8,7 @@
   described_class::RESTRICT_ON_SEND.each_with_index do |validation, number|
     it "registers an offense for #{validation}" do
       offenses = inspect_source("#{validation} :name")
-      expect(offenses.first.message).to include(described_class::ALLOWLIST[number])
+      expect(offenses.first.message.include?(described_class::ALLOWLIST[number])).to be(true)
     end
   end