Fix falsy offense for Style/RedundantSelf with pseudo variables

[pocke]

Problem

RuboCop says "Redundant self detected" for self.__FILE__, but the self cannot be omitted.

class A
  def __FILE__
    '__FILE__ method'
  end

  def __LINE__
    '__LINE__ method'
  end

  def __ENCODING__
    '__ENCODING__ method'
  end

  def a
    p self.__FILE__
    p __FILE__
    p self.__LINE__
    p __LINE__
    p self.__ENCODING__
    p __ENCODING__
  end
end

A.new.a

$ ruby test.rb
"__FILE__ method"
"test.rb"
"__LINE__ method"
18
"__ENCODING__ method"
#<Encoding:UTF-8>

$ rubocop --only RedundantSelf
Inspecting 1 file
C

Offenses:

test.rb:15:7: C: Style/RedundantSelf: Redundant self detected.
    p self.__FILE__
      ^^^^^^^^^^^^^
test.rb:17:7: C: Style/RedundantSelf: Redundant self detected.
    p self.__LINE__
      ^^^^^^^^^^^^^
test.rb:19:7: C: Style/RedundantSelf: Redundant self detected.
    p self.__ENCODING__
      ^^^^^^^^^^^^^^^^^

1 file inspected, 3 offenses detected

Solution

Add pseudo variables to the keyword list.

---

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• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Run rake default or rake parallel. It executes all tests and RuboCop for itself, and generates the documentation.

[garettarrowood]

Makes sense to me.