Fix false positive for RSpec/EmptyExampleGroup cop with iterator and simple conditional

[lovro-bikic]

Fixes a false positive for RSpec/EmptyExampleGroup with iterator and simple conditional (one that doesn't have multiple statements, so it's not wrapped in a begin node).

Previously, code such as:

context 'foo' do
  [1, 2, 3].each do |x|
    if x.odd?
      it { expect(x).to be_odd }
    else
      it { expect(x).to be_even }
    end
  end
end

would register as an offense. With this patch, the offense isn't registered anymore.

---

Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Updated documentation.
• Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

[pirj]

Thank you

[ydah]

Thank you!