Fix Style/ClassEqualityComparison autocorrection within module

[r7kamura]

In the situation where Module.nesting is not empty, bar.class.name == 'Bar' and bar.instance_of?(Bar) yield different results.

This is a simple example of the problematic case:
(In reality, it is more complicated because constant search is done by tracing back to ancestor inheritance tree)

module Foo
  class << self
    def bar1?(value)
      value.instance_of?(Bar)
    end

    def bar2?(value)
      value.class.name == 'Bar'
    end
  end

  class Bar
  end
end

class Bar
end

p Foo.bar1?(Bar.new) #=> false
p Foo.bar1?(Foo::Bar.new) #=> true

p Foo.bar2?(Bar.new) #=> true
p Foo.bar2?(Foo::Bar.new) #=> false

So I changed it to prepend :: in those situations.

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• 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.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.

[koic]

Good catch! Thanks!