Merging if expression with unless modifier might change original logic. Should be safe fix

[jlahtinen]

Tested with current master 3dc4e62 and 1.6.1
no .rubocop.yml file

Testfile

class Bar
  def bar
    if @a
      raise Foo unless @b && @c
    end
  end
end

after rubocop -a

class Bar
  def bar
    raise Foo if @a && !@b && @c
  end
end

expected

raise line should be e.g. raise Foo if @a && !(@b && @c)