Fix build error

This commit fixes the following `RSpec/FactoryBot/CreateList` error.

```console
% cd path/to/rubocop-rake
% bundle exec rake
(snip)

An error occurred while RSpec/FactoryBot/CreateList cop was inspecting
/Users/koic/src/github.com/rubocop-hq/rubocop-rake/spec/spec_helper.rb:15:15.
To see the complete backtrace run rubocop -d.
```

.rubocop.yml

@@ -45,3 +45,8 @@ RSpec/ExampleLength:
 Naming/FileName:
   Exclude:
     - 'lib/rubocop-rake.rb'
+
+# This disabling is a workaround for https://github.com/rubocop-hq/rubocop-rspec/issues/1068.
+# The cop has been disabled because FactoryBot is not used in this repository.
+RSpec/FactoryBot/CreateList:
+  Enabled: false