Nested method definition inside class << obj is reported as offense

[buehmann]

One false positive of Lint/NestedMethodDefinition was not covered by the fix for #4185:

class Foo
  def x(obj)
    class << obj
      def y
      end
    end
  end
end

bug.rb:4:7: W: Method definitions must not be nested. Use lambda instead.
      def y ...
      ^^^^^

Expected behavior

I expect RuboCop not do register an offense for nested defs like these.

RuboCop version

Include the output of rubocop -V. Here's an example:

$ rubocop -V
0.48.0 (using Parser 2.4.0.0, running on ruby 2.3.1 x86_64-darwin15)