Don't use Include in rubocop configuration file

The Rakefile and config.ru files are now included by default, and the
behaviour of `Include` changed in Rubocop 0.56.0 (see rubocop's pull
request 5882) so now it **only** includes the files defined there, while
in the past it included those files in addition to the default files.

.rubocop_basic.yml

@@ -3,9 +3,6 @@ require: rubocop-rspec
 AllCops:
   DisplayCopNames: true
   DisplayStyleGuide: true
-  Include:
-    - "**/Rakefile"
-    - "**/config.ru"
   Exclude:
     - "db/migrate/**/*"
     - "db/schema.rb"