Duplicate nested element

When you have an element inside another with the same name, it broke :)

```xml
<root>
  <feature>
    <feature>1</feature>
    <feature>2</feature>
  </feature>
</root>
```

Ends up returning this hash:

```ruby
{
  "root" => {
    "feature" => [{}, 1, 2]
  }
}
```

I [removed an `if`](https://github.com/sumavisos/bliss/commit/cae8effa0bb166504d55814fab470c6dc4159f0a) that seems to ignore this case, though I'm not 100% sure this breaks something. But this spec passes, and the other specs are also good.