Keys of hash inside array is not symbolized.

```xml
<users><user name="Erik Michaels-Ober"/><user><name>Wynn Netherland</name></user></users>
```
is now parsed into
```ruby
{:users=>{:user=>[{"name"=>"Erik Michaels-Ober"}, {"name"=>"Wynn Netherland"}]}}
```
even if symbolize_keys is true.