Use RuboCop RSpec 2.18

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

```console
% bundle exec rake
(snip)

Offenses:

spec/project_spec.rb:20:9: C: [Correctable] RSpec/PredicateMatcher: Prefer using include? over include matcher.
        expect(description).not_to include("\n")
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
spec/rubocop/cop/performance/times_map_spec.rb:5:13: C: [Correctable] RSpec/ContextMethod: Use describe for testing methods.
    context ".times.#{method}" do
            ^^^^^^^^^^^^^^^^^^

115 files inspected, 2 offenses detected, 2 offenses autocorrectable
RuboCop failed!
```

Gemfile

@@ -10,7 +10,7 @@ gem 'bump', require: false
 gem 'rake'
 gem 'rspec'
 gem 'rubocop', github: 'rubocop/rubocop'
-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

@@ -17,7 +17,7 @@
       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/performance/times_map_spec.rb

@@ -2,7 +2,7 @@
 
 RSpec.describe RuboCop::Cop::Performance::TimesMap, :config do
   shared_examples 'map_or_collect' do |method|
-    context ".times.#{method}" do
+    describe ".times.#{method}" do
       context 'with a block' do
         it 'registers an offense and corrects' do
           expect_offense(<<~RUBY, method: method)