False positive in Rails/FilePath cop

[lucascaton]

Expected behavior

Rails/FilePath cop (PR) shouldn't complain when I have the following code:

system "rm -rf #{Rails.root.join('public', 'system')}"

Actual behavior

$ rubocop --only Rails/FilePath

Offenses:
lib/tasks/db.rake:52:12: C: Rails/FilePath: Please use Rails.root.join('path', 'to') instead.
    system "rm -rf #{Rails.root.join('public', 'system')}"
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

RuboCop version

0.47.1 (using Parser 2.3.3.1, running on ruby 2.3.3 x86_64-darwin16)

Thank you.